Can you use an external microphone for music lessons on FaceTime.

Hello, Perll.

Thank you for using Apple Support Communities.

From your post, we understand you're having troubles with microphone clarity on your iPhone. We'd be glad to help out. We'd recommend confirming if the issue is indeed with your microphone, check out this article and follow the steps to test: If the microphones on your iPhone aren't working

Connection issues or poor connections can also cause sound to not be clear during FaceTime calls. Try connecting to a different Wi-Fi network or use cellular data to see if that helps. This could also be on the receivers end as well. This article has some great information: Resolve Wi-Fi and Bluetooth issues caused by wireless interference

To answer your question, yes you can use external microphones with the iPhone.

Best regards.