diff --git a/packages/ui/src/App.tsx b/packages/ui/src/App.tsx
index 7475c486..d19a5da3 100644
--- a/packages/ui/src/App.tsx
+++ b/packages/ui/src/App.tsx
@@ -1,6 +1,7 @@
 import { Component, For, Show, createMemo, createEffect, createSignal, onMount, onCleanup } from "solid-js"
 import { Dialog } from "@kobalte/core/dialog"
 import { Toaster } from "solid-toast"
+import useMediaQuery from "@suid/material/useMediaQuery"
 import AlertDialog from "./components/alert-dialog"
 import FolderSelectionView from "./components/folder-selection-view"
 import { showConfirmDialog } from "./stores/alerts"
@@ -82,6 +83,46 @@ const App: Component = () => {
   const [remoteAccessOpen, setRemoteAccessOpen] = createSignal(false)
   const [instanceTabBarHeight, setInstanceTabBarHeight] = createSignal(0)
 
+  const phoneQuery = useMediaQuery("(max-width: 767px)")
+  const isPhoneLayout = createMemo(() => phoneQuery())
+
+  // In-memory only: hides chrome on phone; may also request browser fullscreen.
+  const [mobileFullscreenMode, setMobileFullscreenMode] = createSignal(false)
+  const [browserFullscreenActive, setBrowserFullscreenActive] = createSignal(false)
+
+  const fullscreenSupported = () => {
+    if (typeof document === "undefined") return false
+    const el = document.documentElement as any
+    return Boolean(document.fullscreenEnabled) && typeof el?.requestFullscreen === "function"
+  }
+
+  const syncBrowserFullscreenState = () => {
+    if (typeof document === "undefined") return
+    setBrowserFullscreenActive(Boolean(document.fullscreenElement))
+  }
+
+  const enterMobileFullscreen = async () => {
+    if (!isPhoneLayout()) return
+    setMobileFullscreenMode(true)
+    if (!fullscreenSupported()) return
+    try {
+      await document.documentElement.requestFullscreen()
+    } catch {
+      // Ignore: immersive mode still works without browser fullscreen.
+    }
+  }
+
+  const exitMobileFullscreen = async () => {
+    if (typeof document !== "undefined" && document.fullscreenElement && typeof document.exitFullscreen === "function") {
+      try {
+        await document.exitFullscreen()
+      } catch {
+        // Ignore
+      }
+    }
+    setMobileFullscreenMode(false)
+  }
+
   createEffect(() => {
     if (typeof document === "undefined") return
     const shouldShow =
@@ -95,6 +136,31 @@ const App: Component = () => {
     setInstanceTabBarHeight(element?.offsetHeight ?? 0)
   }
 
+  onMount(() => {
+    if (typeof document === "undefined") return
+    syncBrowserFullscreenState()
+    document.addEventListener("fullscreenchange", syncBrowserFullscreenState)
+    onCleanup(() => document.removeEventListener("fullscreenchange", syncBrowserFullscreenState))
+  })
+
+  // If the user exits browser fullscreen via browser UI, restore chrome.
+  let lastBrowserFullscreen = false
+  createEffect(() => {
+    const active = browserFullscreenActive()
+    const mode = mobileFullscreenMode()
+    if (mode && lastBrowserFullscreen && !active) {
+      setMobileFullscreenMode(false)
+    }
+    lastBrowserFullscreen = active
+  })
+
+  // If we leave phone layout (rotation / resize), restore chrome.
+  createEffect(() => {
+    if (!isPhoneLayout() && mobileFullscreenMode()) {
+      void exitMobileFullscreen()
+    }
+  })
+
   createEffect(() => {
     void initMarkdown(isDark()).catch((error) => log.error("Failed to initialize markdown", error))
   })
@@ -410,14 +476,16 @@ const App: Component = () => {
           when={!hasInstances()}
           fallback={
             <>
-              <InstanceTabs
-                instances={instances()}
-                activeInstanceId={activeInstanceId()}
-                onSelect={setActiveInstanceId}
-                onClose={handleCloseInstance}
-                onNew={handleNewInstanceRequest}
-                onOpenRemoteAccess={() => setRemoteAccessOpen(true)}
-              />
+              <Show when={!isPhoneLayout() || !mobileFullscreenMode()}>
+                <InstanceTabs
+                  instances={instances()}
+                  activeInstanceId={activeInstanceId()}
+                  onSelect={setActiveInstanceId}
+                  onClose={handleCloseInstance}
+                  onNew={handleNewInstanceRequest}
+                  onOpenRemoteAccess={() => setRemoteAccessOpen(true)}
+                />
+              </Show>
  
               <For each={Array.from(instances().values())}>
                 {(instance) => {
@@ -435,7 +503,10 @@ const App: Component = () => {
                             handleSidebarAgentChange={(sessionId, agent) => handleSidebarAgentChange(instance.id, sessionId, agent)}
                             handleSidebarModelChange={(sessionId, model) => handleSidebarModelChange(instance.id, sessionId, model)}
                             onExecuteCommand={executeCommand}
-                            tabBarOffset={instanceTabBarHeight()}
+                            tabBarOffset={isPhoneLayout() && mobileFullscreenMode() ? 0 : instanceTabBarHeight()}
+                            mobileFullscreenMode={isPhoneLayout() && mobileFullscreenMode()}
+                            onEnterMobileFullscreen={() => void enterMobileFullscreen()}
+                            onExitMobileFullscreen={() => void exitMobileFullscreen()}
                           />
                         </InstanceMetadataProvider>
 
diff --git a/packages/ui/src/components/instance/instance-shell2.tsx b/packages/ui/src/components/instance/instance-shell2.tsx
index 5238159b..3c6fa711 100644
--- a/packages/ui/src/components/instance/instance-shell2.tsx
+++ b/packages/ui/src/components/instance/instance-shell2.tsx
@@ -42,7 +42,7 @@ import { useSessionSidebarRequests } from "./shell/useSessionSidebarRequests"
 import RightPanel from "./shell/right-panel/RightPanel"
 import { useDrawerChrome } from "./shell/useDrawerChrome"
 import { getSessionStatus } from "../../stores/session-status"
-import { ShieldAlert } from "lucide-solid"
+import { Maximize2, Minimize2, ShieldAlert } from "lucide-solid"
 
 import type { LayoutMode } from "./shell/types"
 import {
@@ -70,6 +70,11 @@ interface InstanceShellProps {
   handleSidebarModelChange: (sessionId: string, model: { providerId: string; modelId: string }) => Promise<void>
   onExecuteCommand: (command: Command) => void
   tabBarOffset: number
+
+  // In-memory only: mobile immersive/fullscreen mode.
+  mobileFullscreenMode: boolean
+  onEnterMobileFullscreen: () => void
+  onExitMobileFullscreen: () => void
 }
 
 const InstanceShell2: Component<InstanceShellProps> = (props) => {
@@ -118,6 +123,7 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
   })
 
   const isPhoneLayout = createMemo(() => layoutMode() === "phone")
+  const mobileFullscreen = createMemo(() => props.mobileFullscreenMode && isPhoneLayout())
   const leftPinningSupported = createMemo(() => layoutMode() !== "phone")
   const rightPinningSupported = createMemo(() => layoutMode() !== "phone")
 
@@ -585,13 +591,14 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
       {renderLeftPanel()}
 
       <Box sx={{ display: "flex", flexDirection: "column", flex: 1, minWidth: 0, minHeight: 0, overflowX: "hidden" }}>
-        <AppBar position="sticky" color="default" elevation={0} class="border-b border-base">
-          <Toolbar variant="dense" class="session-toolbar flex flex-wrap items-center gap-2 py-0 min-h-[40px]">
-            <Show
-              when={!isPhoneLayout()}
-              fallback={
-                <div class="flex flex-col w-full gap-1.5">
-                  <div class="flex flex-wrap items-center justify-between gap-2 w-full">
+        <Show when={!mobileFullscreen()}>
+          <AppBar position="sticky" color="default" elevation={0} class="border-b border-base">
+            <Toolbar variant="dense" class="session-toolbar flex flex-wrap items-center gap-2 py-0 min-h-[40px]">
+              <Show
+                when={!isPhoneLayout()}
+                fallback={
+                  <div class="flex flex-col w-full gap-1.5">
+                    <div class="flex flex-wrap items-center justify-between gap-2 w-full">
                     <Show when={leftDrawerState() === "floating-closed"}>
                       <IconButton
                         ref={setLeftToggleButtonEl}
@@ -638,6 +645,18 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
                       </span>
                     </div>
 
+                    <Show when={!props.mobileFullscreenMode}>
+                      <IconButton
+                        color="inherit"
+                        onClick={props.onEnterMobileFullscreen}
+                        aria-label={t("instanceShell.fullscreen.enter")}
+                        title={t("instanceShell.fullscreen.enter")}
+                        size="small"
+                      >
+                        <Maximize2 class="w-5 h-5" aria-hidden="true" />
+                      </IconButton>
+                    </Show>
+
                     <Show when={rightDrawerState() === "floating-closed"}>
                       <IconButton
                         ref={setRightToggleButtonEl}
@@ -750,9 +769,24 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
                   </Show>
                 </div>
               </div>
-            </Show>
-          </Toolbar>
-        </AppBar>
+              </Show>
+            </Toolbar>
+          </AppBar>
+        </Show>
+
+        <Show when={mobileFullscreen()}>
+          <div class="mobile-fullscreen-exit-wrapper">
+            <button
+              type="button"
+              class="message-scroll-button mobile-fullscreen-exit-button"
+              onClick={props.onExitMobileFullscreen}
+              aria-label={t("instanceShell.fullscreen.exit")}
+              title={t("instanceShell.fullscreen.exit")}
+            >
+              <Minimize2 class="h-5 w-5" aria-hidden="true" />
+            </button>
+          </div>
+        </Show>
 
         <Box
           component="main"
diff --git a/packages/ui/src/lib/i18n/messages/en/instance.ts b/packages/ui/src/lib/i18n/messages/en/instance.ts
index 7a25118a..d8b02bbc 100644
--- a/packages/ui/src/lib/i18n/messages/en/instance.ts
+++ b/packages/ui/src/lib/i18n/messages/en/instance.ts
@@ -39,6 +39,9 @@ export const instanceMessages = {
   "instanceShell.rightDrawer.toggle.open": "Open right drawer",
   "instanceShell.rightDrawer.toggle.close": "Close right drawer",
 
+  "instanceShell.fullscreen.enter": "Full screen",
+  "instanceShell.fullscreen.exit": "Exit full screen",
+
   "instanceShell.metrics.usedLabel": "Used",
   "instanceShell.metrics.availableLabel": "Avail",
 
diff --git a/packages/ui/src/lib/i18n/messages/es/instance.ts b/packages/ui/src/lib/i18n/messages/es/instance.ts
index b88d99bf..7fa214eb 100644
--- a/packages/ui/src/lib/i18n/messages/es/instance.ts
+++ b/packages/ui/src/lib/i18n/messages/es/instance.ts
@@ -39,6 +39,9 @@ export const instanceMessages = {
   "instanceShell.rightDrawer.toggle.open": "Abrir panel derecho",
   "instanceShell.rightDrawer.toggle.close": "Cerrar panel derecho",
 
+  "instanceShell.fullscreen.enter": "Pantalla completa",
+  "instanceShell.fullscreen.exit": "Salir de pantalla completa",
+
   "instanceShell.metrics.usedLabel": "Usado",
   "instanceShell.metrics.availableLabel": "Disp.",
 
diff --git a/packages/ui/src/lib/i18n/messages/fr/instance.ts b/packages/ui/src/lib/i18n/messages/fr/instance.ts
index 09f2ee28..8d752464 100644
--- a/packages/ui/src/lib/i18n/messages/fr/instance.ts
+++ b/packages/ui/src/lib/i18n/messages/fr/instance.ts
@@ -39,6 +39,9 @@ export const instanceMessages = {
   "instanceShell.rightDrawer.toggle.open": "Ouvrir le tiroir droit",
   "instanceShell.rightDrawer.toggle.close": "Fermer le tiroir droit",
 
+  "instanceShell.fullscreen.enter": "Plein écran",
+  "instanceShell.fullscreen.exit": "Quitter le plein écran",
+
   "instanceShell.metrics.usedLabel": "Utilisé",
   "instanceShell.metrics.availableLabel": "Dispo",
 
diff --git a/packages/ui/src/lib/i18n/messages/ja/instance.ts b/packages/ui/src/lib/i18n/messages/ja/instance.ts
index 04a48938..9b24edc8 100644
--- a/packages/ui/src/lib/i18n/messages/ja/instance.ts
+++ b/packages/ui/src/lib/i18n/messages/ja/instance.ts
@@ -39,6 +39,9 @@ export const instanceMessages = {
   "instanceShell.rightDrawer.toggle.open": "右ドロワーを開く",
   "instanceShell.rightDrawer.toggle.close": "右ドロワーを閉じる",
 
+  "instanceShell.fullscreen.enter": "全画面",
+  "instanceShell.fullscreen.exit": "全画面を終了",
+
   "instanceShell.metrics.usedLabel": "使用",
   "instanceShell.metrics.availableLabel": "残り",
 
diff --git a/packages/ui/src/lib/i18n/messages/ru/instance.ts b/packages/ui/src/lib/i18n/messages/ru/instance.ts
index 17d4ec36..90ca86f4 100644
--- a/packages/ui/src/lib/i18n/messages/ru/instance.ts
+++ b/packages/ui/src/lib/i18n/messages/ru/instance.ts
@@ -39,6 +39,9 @@ export const instanceMessages = {
   "instanceShell.rightDrawer.toggle.open": "Открыть правую панель",
   "instanceShell.rightDrawer.toggle.close": "Закрыть правую панель",
 
+  "instanceShell.fullscreen.enter": "Полный экран",
+  "instanceShell.fullscreen.exit": "Выйти из полного экрана",
+
   "instanceShell.metrics.usedLabel": "Использовано",
   "instanceShell.metrics.availableLabel": "Доступно",
 
diff --git a/packages/ui/src/lib/i18n/messages/zh-Hans/instance.ts b/packages/ui/src/lib/i18n/messages/zh-Hans/instance.ts
index a978e220..9143fb57 100644
--- a/packages/ui/src/lib/i18n/messages/zh-Hans/instance.ts
+++ b/packages/ui/src/lib/i18n/messages/zh-Hans/instance.ts
@@ -39,6 +39,9 @@ export const instanceMessages = {
   "instanceShell.rightDrawer.toggle.open": "打开右侧抽屉",
   "instanceShell.rightDrawer.toggle.close": "关闭右侧抽屉",
 
+  "instanceShell.fullscreen.enter": "全屏",
+  "instanceShell.fullscreen.exit": "退出全屏",
+
   "instanceShell.metrics.usedLabel": "已用",
   "instanceShell.metrics.availableLabel": "可用",
 
diff --git a/packages/ui/src/styles/panels/session-layout.css b/packages/ui/src/styles/panels/session-layout.css
index 845f7c69..f03cf6a7 100644
--- a/packages/ui/src/styles/panels/session-layout.css
+++ b/packages/ui/src/styles/panels/session-layout.css
@@ -125,6 +125,18 @@ session-sidebar-controls .selector-trigger-primary {
   width: 100%;
 }
 
+.mobile-fullscreen-exit-wrapper {
+  position: fixed;
+  top: calc(env(safe-area-inset-top, 0px) + 12px);
+  right: calc(env(safe-area-inset-right, 0px) + 12px);
+  z-index: 1250;
+  pointer-events: none;
+}
+
+.mobile-fullscreen-exit-button {
+  pointer-events: auto;
+}
+
 .session-resize-handle {
   @apply absolute top-0 w-1 h-full cursor-col-resize bg-transparent transition-colors;
   z-index: 10;