When I call, or receive calls, while in my car the phone has stopped playing audio through my speakers. I have to touch the speaker phone button in order for it to play through the speakers. I have it attached via an audio cable. Ask other sounds like texts, music, etc. okay through fine. Tried other cables no luck. Just started happening.
I Find updates mess up setting all the time. You may have to dump cache data and set up again.
( I had a similar problem a while back when Google Maps stopped working with my Samsung phone)
MY drive mode allows only preset callers through
calls via bluetooth
calls via headset.
IF you review or reset these settings, they may have changed (gotta love updates). You should be able to reset the app settings without resetting the entire phone.