Using Screen Time you can get an overview of how much you use your phone and set time limits on the use of selected apps.
Press Screen Time.
Press Turn On Screen Time.
Press This is My iPhone.
Press the indicator next to "Downtime" and follow the instructions on the screen to select Downtime period.
Press App Limits.
Press Add Limit.
Press the required categories.
Set the required time limit for use of the selected category.
Press Customise Days.
Press the required days.
Select the required period.
Press Delete Limit.
Press Always Allowed.
Press the add icon next to the required app to add it to the list of allowed apps during Downtime.
Press the remove icon next to the required app to remove it from the list of allowed apps during Downtime.
Press Content & Privacy Restrictions.
Press the indicator next to "Content & Privacy Restrictions" and follow the instructions on the screen to select settings for content and privacy restrictions.
Press arrow left.
Press Use Screen Time Passcode and follow the instructions on the screen to select a Screen Time password.
Press the Home key to return to the home screen.