if i lock my mobile keypad than mobile is restaring

Hello hameedgazgi,

If we understand correctly, your iPhone is restarting on it's own when you lock the device, correct?

If so, check your iPhones Battery Health to see if your battery needs to be replaced. To check, go to Settings > Battery > Battery Health.

You should see your battery health, along with a message about performance in the Peak Performance Capability section. This will either say "Your battery is currently supporting normal peak performance" or "This iPhone has experienced an unexpected shutdown because the battery was unable to deliver the necessary peak power. Performance management has been applied to help prevent this from happening again." iPhone Battery and Performance - Apple Support

If the battery does need to be replaced, you can locate service and pricing here: iPhone Repair & Service - Apple Support

Let us know what you find! Take care.