I recently had all these cars with BT: Subaru Legacy, Toyota Corolla, Mazda CX-5.
With my device (the antique
Treo Pro) I have also found the phone sets up easier than the audio. I discovered in BT settings an option to "set as wireless stereo". But I have to connect the phone first, then "set as wireless stereo".
Based on my experience and informal discussions with others
when the problem is that the phone works but the audio doesn't I am inclined to suspect the issue lies in the handheld device's BT rather than in the vehicle.