iphone 7 hands free operation in car

Until recently this worked fine. Then about 2 months ago, when receiving incoming calls the sound -- ringtone, speech -- no longer came through the car's speakers but came from the phone. Everything else works normally e.g. contacts list, recent calls etc all display in car 's screen and radio mutes.

If during a call, I tap the 'audio' icon on the phone's screen it shows the default setting as 'phone'. If I then select the option of 'my car' then speech does come through the car's speakers i.e. works correctly. However, this setting is not retained by the phone and this process has to be done every time a call comes in. This of course means it is no longer a hands free operation so I can no longer use my phone in the car.

This problem arose around time I upgraded the software to i12.4; it has continued after upgrading to 12.4.1.

Has anyone else encountered this problem and is there a solution?

baffledbobtail