Unfortunately, iPhones don't currently offer a way to independently choose audio outputs (speakers) and microphone inputs while connected to Bluetooth.
- If your car stereo has an auxiliary input port (Aux In), you can use a Lightning to Aux cable to connect your iPhone directly. This would bypass Bluetooth altogether and likely use the phone's microphone for calls and recordings.
- Check if your car stereo has an option to select audio sources. Some car stereos allow you to choose between Bluetooth audio and phone audio sources. If available, select the phone audio source.
- If you have AirPods or another Bluetooth headset with a microphone, you can connect them to your phone while still connected to the car stereo via Bluetooth. This would allow calls and recordings to use the headset's microphone while music plays through the car speakers.
Keep in mind that the available options might vary depending on your car stereo model, iOS version, and the specific apps you're using.
While there isn't a perfect solution yet, hopefully one of these options helps you use your phone's microphone for calls and recordings while keeping your car stereo connected for music playback.