I phone 7

Hi, Bill,

Thanks for visiting the Apple Support Communities. It sounds like when you make or receive a call, the other person cannot hear you until you select the audio button and switch the device to the iPhone. I'm happy to help!

Typically, the audio button appears when you have a Bluetooth device, like earphones, connected to your iPhone. In this instance, an incoming or outgoing call would default audio to the Bluetooth device instead of the phone's speaker and microphone. Tapping the audio button lets you toggle between the Bluetooth device, your phone's receiver and microphone, or your phone's speakerphone and microphone. You can also disconnect your Bluetooth device: While on a call on iPhone - Apple Support.

If the issue you're experiencing is that no one can hear you at all, try the steps in If the microphones on your iPhone aren't working - Apple Support.

Best.