Make things right and better by starting afresh. A device restart works in the same way. The difficulty you're having appears to be caused by software faults, therefore if the first proposed remedy doesn't work, you should attempt a restart or soft reset this time. There's no need to be concerned about data loss because this procedure has no effect on the data on your iPhone. Here's how you do it:

1. For a few seconds, press and hold the Side/Power button and either Volume button at the same time.
2. Release the buttons when you get the Slide to Power off prompt.
3. To turn your phone off, slide the Power switch to the right.
4. After around 30 seconds, press and hold the Side/Power button until you see the Apple logo.