Bluetooth Audio not Coming from Car Speakers, but Can Control iPhone from the Car

I have this annoying issue with my Bluetooth connection: when I get into the car the display shows my iPhone X is connected and in fact it is listed as connected on the devices list, both as a phone and as an audio player. However, the sound comes only from the iPhone speakers and not from the car speakers, the audio can be paused, move Fwd or back and overall controlled from the car but the audio only comes from the phone. If I place a call or use Siri Eyes Free it is fixed but not always, having me to try many times until the phone connects completely

It suddenly started about six months ago with my old 2011 Prius IV, first with an iPhone 6, then with an iPhone 8 and now with the iPhone X. I thought it was an issue of that BT technology being 7 years old, new iOS, etc. and waited until I got a new Prius Prime, but the issue persisted. It might have to do with the Phone itself but why would that happen? I believe although cannot be absolutely sure, the issue started with the upgrade to iOS 11

Not the big deal but very annoying, I was wondering if someone else is having the same issue. Appreciate any insights. Thanks