Found the solution. Hopefully, this will help others who have also checked off all the typical solutions with no success.
In another thread on this topic (which was closed so I couldn't comment there), a person commented that it turned out they did NOT have LTE service (4G) from their carrier. But, in Settings-->Phone Data they had set the type of service to LTE and not 3G. Once they switched the setting to 3G, they started to receive calls again. I originally ignored this piece of information because I knew we DO have LTE service from Verizon and live where the LTE service is solid. However, and out of desperation, I tried switching my wife's phone setting to 3G. Voila! She immediately started receiving calls again. No voicemail! Because we do have LTE service, I then toggled the switch back to LTE, hoping the solution would stick. It did! So, for whatever reason, toggling the Phone Data switch from LTE to 3G. Make a test call. And then switch back to LTE fixed the problem. Cheers, Mr. Luigi