Whenever I use wireless Android Auto with my S22 Plus Ultra, the sound only comes through my phone speaker, not my car speaker.
This only happens when I am calling/talking with someone, and it doesn't matter if I call someone else or if they call me.
The other apps like Spotify and Navigation apps work fine. The sound comes from my car speakers.
There is a post about it here, but AA says to reach out to the phone manufacturer:
Sounds like your phone is defaulting to the phones speaker when call come in. Check it and see if there's a Bluetooth button when you answer the call click it & it should go back to the radio without disconnecting.