Thanks for bringing your iPhone issue to the Apple Support Communities. If I understand, when on calls neither you nor the other person can hear each other. That is, until you restart your iPhone. I make and receive a lot of phone calls throughout the day, so I know how important it is for the audio to work in both directions. I'm happy to help!
To troubleshoot the issue you're having hearing the person you're on the phone with, I recommend using the steps here: If you can't hear a person on a call or voicemail or if the sound isn't clear on your iPhone - Apple Support .
To troubleshoot issues with the other person hearing you, I recommend using Get help with the microphones on your iPhone, iPad, and iPod touch - Apple Support .
Have a good day.