Safe Mode puts your phone in a diagnostic state (returned to default settings) so you can determine if a third party app is causing your device to freeze, reset or run slow.
Press and hold the Power button.
Touch and hold Power off.
From the Reboot to safe mode screen, tap OK.
The device restarts with Safe mode appearing in the lower left.
This may take up to a minute.
With Safe Mode enabled, test device and app functionality. If the previous issue fails to occur, the cause has been isolated to a third-party app and all recently installed or updated apps should be uninstalled.
Power cycle the device to disable Safe Mode, reinstall then test each app, one at a time, to identify which is causing the problem.