Does this happen in Safe Mode as well? https://support.motorola.com/us/en/solution/MS148713
If it's only making the ringtone softer while you're waiting for the other person to pick up, then at least it's not actually impacting your phone conversations, correct?
I believe I have figured out the reason for the low dial tone on the Moto G Power. My wife's phone does the same thing and I just recently had it happen to me. My phone for the first few days worked normally, then all of a sudden, my volume level dropped when making a call. For whatever reason, I pushed my volume control button on the side and the screen popped up 2 different volume settings, one of which was all the way down. Now I promise, it was fully up prior to making the call. I raised it up with my finger and could hear the louder ring. I think what is happening is that it automatically drops lower and is a safety feature so that it DOES NOT hurt your hearing.....that's it!!!