Cannot Hear Text Message Tone New iPhone 12 with iOS 15.1

11/16/2021 - My phone is about a month old. All the other sounds work. I've been using iPhone since the 4 and know how to manage "Do Not Disturb," volume controls, etc.

However, this problem only began in the last week-to-ten days. I have a tone selected for text messages. If my phone is "active" (not dark and "closed") I might hear the tone. However, if the phone is in "rest" mode in my pocket or my holster, it does not come through at all!

Any thoughts?

Thank you!