If I turn the radio volume down when I'm done listening to it and then the phone rings I get no phone volume.
The caller hears me just fine.
I have had to remember to roll up the left wheel when I hear a call coming in.
I have a Note 20 Ultra and just had a Galaxy S20 Ultra and use an iPhone on occasion at work. I used all three in a 2013 Model S, 2017 Model S, 2019 Model S, and the Androids both on a Model Y that's a few weeks old. All of them had this "issue". The difference with the Model Y is that the volume for media turns up when I turn my phone up, where the S' I had to turn the volume up on the phone to have decent volume on the speakers.
My guess is that it's related more to the BLT your car and phone may have.