Same phone, same problem.  Got replacement same phone under warranty - same problem.  When we power off then on the phone is OK for few days, then problem back.  Can "ask google" and get answer so speaker and mic are fine.  Called for support:  Turn off advanced calling: settings:advanced calling.  Problem went away but went to 1x instead of 4G.  Transferred to Verizon level 2 support.  Phone is out of sync with roaming list and hasn't registered with towers.  Technician reloaded phone settings and "forced" something.  Problem appears fixed but will have to follow up in a few days to see if it comes back.