You can hear them, but they can’t hear you?
Well you may need a new microphone.
For iPhones, please be aware that the microphone is attached to your charge port and will be replace. This usually doesn’t cause any issues, but if it does we will replace with a new charge port.
Though rare, please check to see if your case may be causing the issue. It happens.
The other cases are sometimes dust and dirt getting stuck into the microphone grill. We can also take care of that for you.