My iPhone SE has developed a disturbing feature. It usually needs to be restarted to make a phone call successfully. I don’t make many calls (less than one per day generally); as a test, I tried to call a number about a day after a restart and it went through (I assume; I knew no one was there and I hung up as soon as I heard it ring). But most of the time it has been over a day since my last call and I need to shut down and restart before I can actually complete a call.
Failure is indicated by the phone turning off speaker without user intervention, no audible ringing tone, and eventually a failure message from the phone. Attempted calls do appear in the Recents menu.
I did Reset Network Settings to no effect. I have not Reset All Settings. The iOS is version 12.1.4; 12.3.1 is available. (Just out of curiosity, how would I install something greater than 12.1.4 but less than 12.3.1 if I wanted to do that?)
I believe the problem started on a recent trip, during which the phone went without service for about a week, and also during which it indicated that it had only 3G service in both Seattle and New York City. My provider is Virgin Mobile USA.
Suggestions? Comments? Thanks for any help.