How to keep Google Maps sounds in Phone, while calls in Car Sound system, while driving?

I am driving with Google Maps, while Bluetooth on. I cannot hear any Google Maps sounds if Bluetooth is on, my car stereo system is not playing them, while listening radio (I know you could change the input source but I do not want that). So I turn Bluetooth off because then the sounds of Google Maps come from the phone. How can you force all sounds from Google Maps to come from the phone, although you have Bluetooth on and connected to car stereo?