I do exactly the same
I'm not sure Android Auto can kick in over your radio with announcements. If I want to hear stuff over the car audio ('15 Ford Focus) I have to select the phone's Bluetooth as the input. So I'd have to have the radio / music playing from the phone...so I just switch to this if I need to hear anything from the phone.
https://www.pcworld.com/article/3263...n-any-car.html