I don't want my car to answer phone calls (iPhone 7 Plus IOS 12.3.1)

I like playing music in my car through my iphone but absolutely hate that the car automatically overs on all the phone calls. Can this be changed? I can't hear the caller over my speakers without blasting the volume, and they can't hear me unless I shout back. I immediately choose iphone speaker when someone calls me in the car, but a few seconds later the car over-rides my decision and sends it back to the speaker. I've gotten used to it now so I know I have to choose iphone speaker twice, but I always lose whatever the person was saying in the interim, and I have to ask them to repeat themselves. Every. Time. This gets old, and it's dangerous to be fumbling with my phone so much in the car. Please help!