Prius C (Audio/Electronics) :: Talking Prompt On Car Dash Display

I've been using Google Maps on my iPhone 6 through my Prius C1's bluetooth for years, and it's 99% reliable. But only if I'm currently playing music from my phone (using the built-in Music app). If I pause the music, all the turn-by-turn directions invariably come through sounding like a shitty quality phone call. The "Talking..." prompt on the car's dash display also appears, so I'm guessing the car thinks I'm making a phone call, even though I'm not.

This wouldn't be that bad, except that every time a direction prompt sounds, the music pauses for a few seconds, playing through the shitty quality phone mode. This sounds awful, and is the main reason I want to find a solution to this problem. But it's not the only issue.

Strangely enough, if I start a navigation in Google Maps before I get into my car, the bluetooth will treat all the audio coming from my phone, including music, as a shitty quality phone call. The only way to fix it is to shut down the engine and reboot the entire car.

I've done a little bit of experimentation with Apple Maps, and it seems not to suffer from this problem. But I've been using Google Maps for ages, I'm using to the UI, and I trust it a lot more than Apple Maps. I'd much prefer to continue using Google if at all possible.