Ring when phone is locked

I checked all the settings I read about to check as a possible source of the problem, and did not have:

• Do Not Disturb enabled
• The mute side button on
• Notifications not set up properly
• Silence Unknown Callers enabled

After a trip to the Genius Bar, it was fixed by going to Settings>Accessibility>Face ID & Attention and disabling Attention Aware Features. I don't know if I ever enabled that myself or it was enabled in a previous IOS update. I think this is a bug because that is not the expected behavior of this feature.

Also check the mute switch on the side of the phone just above the volume buttons. And, look at Settings>Phone>Silence Unknown callers. If you get a lot of calls from people not in your phone book, you may want to disable that feature.

On a new phone Attention Aware is enabled by default, as most people like the the fact that the phone doesn’t sound loud alerts when they are looking at it. That’s a useful feature if you are in a meeting and have the phone on the table in front of you.

It should ring when locked unless you have enabled Do not Disturb.

Yes, but that is not the way it was working for me. I could lock the phone, put it in my back pocket and it still would not ring. That's why I think it is a bug.