Hello planetscott,
If I'm understanding you right, all of your contacts do not always appear when connecting your iPhone to your car via Bluetooth. I know how important it is to have all of your contacts syncing with your car properly so you can access them easily while driving. I'm happy to help you out with this.
First, if you haven't updated to the most recent version of iOS 13, I recommend doing that now. As of right now, this would be iOS 13.1.3. Keeping your iPhone completely up-to-date ensures your phone gets necessary bug fixes and improvements that will help it run as smoothly as possible. If the issue persists after the update, try out these steps:
- Make sure Settings > Bluetooth > [accessory name] > Sync Contacts, is enabled.
- Toggle Bluetooth off and then back on in Settings > Bluetooth.
- Turn your iPhone off and then back on.
- Delete the pairing record between your car and the stereo. To forget the stereo from your iPhone go to Settings > Bluetooth > [device name] > Forget This Device. You may need to check your car manual to remove your iPhone from your car stereo. Pair and connect the iPhone with your car again.
- Repeat the same steps from step 4, but this time remove all paired devices on the car stereo, including your iPhone. Pair and connect the iPhone with your car again.
- Install any firmware updates on your car stereo.
- Rename your iPhone in Settings > General > About.
Respond back if the issue persists after following those steps.
Thanks for using Apple Support Communities.
Take care!