My phone was a 13 and now a 14 Plus and I am having the same (or a similar) issue. Calls intermittently go straight to voice mail (and don’t show up in missed calls).
The 2 eSIMs didn’t work for me (and the 14 doesn’t have a slot for a physical). I added a month of T-Mobile and still had the problem. I also tried switching to eSIM (on my 13), restarting from new, and later upgrading to a 14 Plus.
The only thing that’s working for me to be able to receive calls is a Verizon network extender. It gives me 4 bars of cellular service instead of 2 bars, and then all calls go through. However, if I turn the extender off, the problem still exists.
And my husband has an Android and he receives all calls, even before the network extender.