Auto lock

1. Is this your corporate iPhone? Then please contact the system administrator of your corporate
2. If it is your personal device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Or please contact the system administrator of the organisation who provided the profile to you

By default, auto-lock will activate when your iPhone is sitting idle for two minutes. You should be able to change that time interval or disable it all together.

To disable it: Tap on Settings > Display & Brightness > Auto Lock > Never

To change the time interval: Tap on Settings > Display & Brightness > Auto Lock > Select the timing that you prefer