diff --git a/src/lib/phone.ts b/src/lib/phone.ts
new file mode 100644
index 0000000..c4fb20f
--- /dev/null
+++ b/src/lib/phone.ts
@@ -0,0 +1,23 @@
+// Mirrors the API's phone rule (radapi schemas._normalize_phone):
+// 7 digits starting with 9 or 7. A 960/+960 country code is stripped ONLY when the
+// number is 10 digits (960 + 7) — a bare 7-digit number like 9601234 is a valid
+// local number and is never stripped.
+
+export const PHONE_ERROR = 'Enter a valid phone number'
+
+/** Returns the normalized 7-digit local number, or null if invalid. */
+export function normalizePhone(raw: string): string | null {
+  let digits = (raw ?? '').replace(/\D/g, '')
+  if (digits.length === 10 && digits.startsWith('960')) {
+    digits = digits.slice(3)
+  }
+  if (digits.length === 7 && (digits[0] === '9' || digits[0] === '7')) {
+    return digits
+  }
+  return null
+}
+
+/** Error message if invalid, else null. */
+export function phoneError(raw: string): string | null {
+  return normalizePhone(raw) === null ? PHONE_ERROR : null
+}
diff --git a/src/pages/Devices.tsx b/src/pages/Devices.tsx
index f408c89..bf49b0b 100644
--- a/src/pages/Devices.tsx
+++ b/src/pages/Devices.tsx
@@ -2,6 +2,7 @@ import { useCallback, useEffect, useState, type ReactNode } from 'react'
 import { Loader2, Pencil, Plus, RefreshCw, Trash2 } from 'lucide-react'
 import { toast } from 'sonner'
 import { api, ApiError, type Device, type DeviceStatus, type Vlan } from '@/lib/api'
+import { normalizePhone, phoneError } from '@/lib/phone'
 import { Button } from '@/components/ui/button'
 import { Badge } from '@/components/ui/badge'
 import { Input } from '@/components/ui/input'
@@ -187,7 +188,8 @@ function AddDeviceDialog({
     }
   }, [open])
 
-  const valid = mac.trim() && group && name.trim() && phone.trim()
+  const phoneErr = phone.trim() ? phoneError(phone) : null
+  const valid = mac.trim() && group && name.trim() && phone.trim() && !phoneErr
 
   async function submit() {
     if (!valid) return
@@ -197,7 +199,7 @@ function AddDeviceDialog({
         mac_address: mac.trim(),
         group,
         name: name.trim(),
-        phone: phone.trim(),
+        phone: normalizePhone(phone) ?? phone.trim(),
         alias: alias.trim() || null,
       })
       toast.success(`Device ${mac.trim()} added`)
@@ -233,8 +235,12 @@ function AddDeviceDialog({
             <Field label="Name" required>
               <Input value={name} onChange={(e) => setName(e.target.value)} />
             </Field>
-            <Field label="Phone" required>
-              <Input value={phone} onChange={(e) => setPhone(e.target.value)} />
+            <Field label="Phone" required error={phoneErr}>
+              <Input
+                placeholder="9XXXXXX"
+                value={phone}
+                onChange={(e) => setPhone(e.target.value)}
+              />
             </Field>
           </div>
           <Field label="Device alias (optional)">
@@ -284,8 +290,10 @@ function EditDeviceDialog({
     }
   }, [device])
 
+  const phoneErr = phone.trim() ? phoneError(phone) : 'Phone is required'
+
   async function submit() {
-    if (!device) return
+    if (!device || phoneErr) return
     setBusy(true)
     try {
       await api.devices.edit({
@@ -293,7 +301,7 @@ function EditDeviceDialog({
         group: group || undefined,
         status,
         name,
-        phone,
+        phone: normalizePhone(phone) ?? phone,
         alias,
       })
       toast.success(`Device ${device.mac_address} updated`)
@@ -337,8 +345,12 @@ function EditDeviceDialog({
             <Field label="Name">
               <Input value={name} onChange={(e) => setName(e.target.value)} />
             </Field>
-            <Field label="Phone">
-              <Input value={phone} onChange={(e) => setPhone(e.target.value)} />
+            <Field label="Phone" error={phoneErr}>
+              <Input
+                placeholder="9XXXXXX"
+                value={phone}
+                onChange={(e) => setPhone(e.target.value)}
+              />
             </Field>
           </div>
           <Field label="Device alias">
@@ -349,7 +361,7 @@ function EditDeviceDialog({
           <Button variant="outline" onClick={onClose}>
             Cancel
           </Button>
-          <Button onClick={submit} disabled={busy}>
+          <Button onClick={submit} disabled={busy || !!phoneErr}>
             {busy && <Loader2 className="h-4 w-4 animate-spin" />}
             Save changes
           </Button>
@@ -414,10 +426,12 @@ function DeleteDeviceDialog({
 function Field({
   label,
   required,
+  error,
   children,
 }: {
   label: string
   required?: boolean
+  error?: string | null
   children: ReactNode
 }) {
   return (
@@ -427,6 +441,7 @@ function Field({
         {required && <span className="text-destructive"> *</span>}
       </Label>
       {children}
+      {error && <p className="text-xs text-destructive">{error}</p>}
     </div>
   )
 }