Probably not switched off but just locked. If it is actually off you will have to press the side button to turn it on, and then the Apple logo appears and after a while you get asked for your password. If it is just locked you swipe up and enter your password.
You can adjust the time before locking in the Display and Brightness setting. But the best thing is to set up Face ID and have it turned on. Then, when the phone is locked, just looking at it while swiping up will unlock it. Occasionally you get asked for the password but not often.
I would temporarily turn auto-lock to never, then get Face ID set up and turned on, then turn auto-lock down to 1 or 2 minutes. The "never" setting is not safe to have on when the phone is not in your hands at home, but it can be useful when making adjustments such as those above as it prevents the phone from locking in the iddle of making changes.
