No incoming call sound on car speakers using iPhone

I've had this issue for a while and provide the solution if others have the same problem.

A call would come through to the car, I'd accept the call but there was no sound on the car speakers. I could just hear the caller on the phone speakers. The caller could hear me.

Turning up the car volume had no effect.

After much web searching I discovered that there is an iPhone setting in Accessibility/Touch/Call Audio Routing giving the options of Automatic/Bluetooth Headset/Speaker.

My phone was set to Speaker (the phone speaker), so the audio would not divert to the car's speakers.

I set it to automatic and Voila! after much searching and head scratching that solved the problem.

I don't know why an iPhone has these options but I guess they are there for a reason.

Hopefully this will help others who have this infuriating and potentially dangerous (in effect you cannot use hands-free) problem.