diff --git a/mobile/app/h/[hostId]/session/[worktreeId].tsx b/mobile/app/h/[hostId]/session/[worktreeId].tsx
index 5b749a41bd8..9deac34cd36 100644
--- a/mobile/app/h/[hostId]/session/[worktreeId].tsx
+++ b/mobile/app/h/[hostId]/session/[worktreeId].tsx
@@ -244,6 +244,7 @@ import {
   getActiveTabIdForHandle,
   isFileExistsErrorMessage,
   isGestureMouseTrackingMode,
+  isTerminalPhoneDisplayMode,
   MOBILE_SESSION_STATUS_LABELS,
   TERMINAL_GESTURE_INPUT_BUCKET_CAPACITY,
   TERMINAL_GESTURE_INPUT_FLUSH_DELAY_MS,
@@ -4167,14 +4168,6 @@ export default function SessionScreen() {
   })
   const closeWithBulkActions = createCloseWithBulkActions(handleCloseSessionTab, bulkCloseActions)
 
-  const isPhoneMode = (handle: string | null): boolean => {
-    if (!handle) {
-      return false
-    }
-    const mode = terminalModes.get(handle)
-    return mode === 'auto' || mode === 'phone' || mode === undefined
-  }
-
   const visibleTabs: MobileSessionTab[] = sessionTabs
   const activeMarkdownTab = activeSessionTab?.type === 'markdown' ? activeSessionTab : null
   const activeFileTab = activeSessionTab?.type === 'file' ? activeSessionTab : null
@@ -4832,12 +4825,12 @@ export default function SessionScreen() {
                         }
                       }}
                       accessibilityLabel={
-                        isPhoneMode(activeHandle)
+                        isTerminalPhoneDisplayMode(activeHandle, terminalModes)
                           ? 'Switch to desktop mode'
                           : 'Switch to phone mode'
                       }
                     >
-                      {isPhoneMode(activeHandle) ? (
+                      {isTerminalPhoneDisplayMode(activeHandle, terminalModes) ? (
                         <Monitor
                           size={14}
                           color={canSend ? colors.textSecondary : colors.textMuted}
@@ -5216,7 +5209,7 @@ export default function SessionScreen() {
           nativeChatTranscriptIsLocalReadable,
           onDismiss: () => setActionTarget(null),
           onToggleChat: toggleTabChatView,
-          isPhoneMode,
+          isPhoneMode: (handle) => isTerminalPhoneDisplayMode(handle, terminalModes),
           onToggleDisplayMode: (handle) => void toggleDisplayMode(handle),
           onRename: setRenameTarget,
           onClear: (target) => void handleClearTerminal(target),
diff --git a/mobile/src/session/mobile-session-route-helpers.test.ts b/mobile/src/session/mobile-session-route-helpers.test.ts
new file mode 100644
index 00000000000..6ae7a930844
--- /dev/null
+++ b/mobile/src/session/mobile-session-route-helpers.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest'
+import { isTerminalPhoneDisplayMode } from './mobile-session-route-helpers'
+
+describe('isTerminalPhoneDisplayMode', () => {
+  it('uses phone mode for automatic, phone, and unreported terminals', () => {
+    const modes = new Map([
+      ['auto', 'auto'],
+      ['phone', 'phone']
+    ] as const)
+
+    expect(isTerminalPhoneDisplayMode('auto', modes)).toBe(true)
+    expect(isTerminalPhoneDisplayMode('phone', modes)).toBe(true)
+    expect(isTerminalPhoneDisplayMode('missing', modes)).toBe(true)
+  })
+
+  it('rejects absent handles and desktop terminals', () => {
+    const modes = new Map([['desktop', 'desktop']] as const)
+
+    expect(isTerminalPhoneDisplayMode(null, modes)).toBe(false)
+    expect(isTerminalPhoneDisplayMode('desktop', modes)).toBe(false)
+  })
+})
diff --git a/mobile/src/session/mobile-session-route-helpers.ts b/mobile/src/session/mobile-session-route-helpers.ts
index 52b277bd6b8..413e1316beb 100644
--- a/mobile/src/session/mobile-session-route-helpers.ts
+++ b/mobile/src/session/mobile-session-route-helpers.ts
@@ -34,6 +34,17 @@ export function isGestureMouseTrackingMode(
   return mode === 'x10' || mode === 'vt200' || mode === 'drag' || mode === 'any'
 }
 
+export function isTerminalPhoneDisplayMode(
+  handle: string | null,
+  terminalModes: ReadonlyMap<string, 'auto' | 'phone' | 'desktop'>
+): boolean {
+  if (!handle) {
+    return false
+  }
+  const mode = terminalModes.get(handle)
+  return mode === undefined || mode === 'auto' || mode === 'phone'
+}
+
 export function getActiveTabIdForHandle(
   tabs: ReadonlyArray<{ id: string; type: string; terminal?: string | null }>,
   terminalHandle: string | null