Calls going straight to voice mail

I've had the same issue for awhile. Randomly, calls would go straight to VM. Rebooting the phone would fix the problem for awhile, then it would start happening again. This was occurring on my (and my wife's) iPhone 7, then as of late, on our iPhone 12's. We did not have Do not Disturb, or Call Forwarding or Silence Unknown callers on, nor was the side button mute switch on. We are Verizon customers.

My latest "fix" is to reset the iPhone's network settings (Settings / General / Reset / Reset Network Settings). My wife and I also had "Calls on other Devices" enabled. (Settings / Phone / Calls on other Devices). I disabled that feature and also turned it off on all my associated devices (iPad and MacBook Pro).

The problem has not reoccurred for five days now, which I hope means its fixed. I wonder if there is an issue with "Calls on other Devices"? That is a very handy feature and I sure would like it to work.