for the second time this week my phone spontaneously does not allow me to call out or accept calls but a caller can leave a message I can play

Any thoughts, my iphone spontaneously stops allowing calls coming in or dialing out ? When I try to accept an incoming call no one can hear me. They are able to leave voicemails that I can play back???

also the phone worked when I got in my car as I could operate the iphone on the car speaker phone But today the car was hundreds of miles away.

the other day a tech person in a shop disconnect from my car but not so today

any help ideas? confounding.