When you stop using your iPhone without pressing the lock screen button, It is usually over a period of time. The system will automatically lock the screen. It is to enter sleep mode. The automatic screen lock time is defaulted to 1 minute. You can adjust the automatic screen lock time. When inactivity can range from 30 seconds to 5 minutes, or you can set it to never lock the screen. Let’s set a time that works for your usage.
On the Home screen, tap [Settings].
Then tap [Display&Brightness].
Tap the [Auto-Lock] item on the screen. Display&Brightness.
When you are trying as tap the time you want. It is auto lock screen, then check mark. It will be displayed after the time list you selected. if itenabled Low Power Mode (Low Power Mode) Automatic screen lock time is always set to 30 seconds.