Hello GardenerUT,
Thank you for using Apple Support Communities.
We understand that you are having an issue with using FaceTime and the microphone not working on your iPhone. It looks like you were able to locate the following article and complete some of those steps: If the microphones on your iPhone aren't working - Apple Support
Next, we'd like to have you try making a FaceTime call using headphones, so that we can fully isolate this to the FaceTime app itself. When using the headphone's microphone, does the same behavior occur? If so, let's remove the FaceTime app using: Delete built-in Apple apps from the Home screen on your iOS 14 or iPadOS device or Apple Watch - Apple Support
Once complete, reinstall the FaceTime app. You may need to reactivate FaceTime by going to Settings > FaceTime. Let us know the results, and we'll go from there.
Best regards.