Hi 59dinpa,
I understand that when answering a call on your iPhone connected to your car via bluetooth, you manually have to select your car stereo to use it's microphone. You can try forgetting the car stereo from the Bluetooth settings on your iPhone, then pairing it up again.
To unpair a Bluetooth accessory, tap Settings > Bluetooth, find the device you want to unpair, and tap
, then Forget this Device.
When you Forget this Device on your iPhone, iPad, or iPod touch, that accessory is removed from the list of available Bluetooth devices. To add the Bluetooth accessory to your device again, place it back in discovery mode and repeat the steps above to pair it again.
- On your iOS device, tap Settings > Bluetooth. Stay on this screen until you complete the steps to pair your accessory.
- Place your accessory in discovery mode and wait for it to appear on your iOS device. If you don't see it or aren't sure how to make it discoverable, check the instructions that came with your accessory or contact the manufacturer.
- Tap your accessory to pair. You might need to enter the PIN or passkey. If you aren't sure what your PIN or passkey is, check the documentation for your accessory.
When pairing is complete, you can use the Bluetooth accessory with your device. You can pair multiple Bluetooth accessories with your iOS device. Just follow the steps above to pair additional accessories.
Set up and use third-party Bluetooth accessories
Thanks for using Apple Support Communities to post your question. Following the steps above should have your iPhone and car stereo's bluetooth connection and settings working as expected.
Have a nice day.