Howdy MicPG,
Thanks for using the Apple Support Communities! I understand that you are able to pair your iPhone with your Toyota and make calls, but not able to play music. Let’s take a look and see what we can do. I'm happy to help!
Let's try to take a look at this resource how to use Control Center. This is where you can ensure your car is selected as your audio output when connected via Bluetooth.
Access and customize Control Center on your iPhone and iPod touch
"Audio"
Open Control Center. Touch and hold the audio card in the upper-right corner of Control Center to quickly play, pause, and control the volume of your favorite song, podcast, and more.
Tap the AirPlay icon (pictured below) to switch the audio output to speakers, headphones, Apple TV, or another audio device. You can also choose to play the same music across multiple speakers you have set up in your home.
You might also see cards for nearby devices that you can control audio playback for. Just tap a card to control audio for that device. You can also use the cards to create a shared music queue with friends.
Also, please try to turn up the volume locally on the iPhone as well as through the car stereo.
Please respond back if you continue to have any issues.
Best regards!