Samsung Galaxy S4: Rings but caller/receiver can't hear:
Question: Was this phone paired with a Bluetooth device like a headset or to a car? It may be stuck to that..
In any case, try holding down the power button, select reset or power off, let the phone reboot. Then try calling someone or have someone call you to test. It should work..
If not, by default Google's "OK Google" voice search maybe the culprit. Try turning it off and see if that works..
"From the home screen, hold down the menu button which should go into Google Now. Click on menu button again and select settings. Select "VOICE." Then select "Ok Google" detection. Once there, switch off the option "From any Screen." Once that is turned off. Restart phone"
If this does not work for you, try calling your Cellular Service Provider and ask them to reset the connection on their side to your phone.,. While they do that, they may ask you to power off your phone, take out the battery, take out the SIM card, wait for at least 30 seconds before re-inserting your SIM card and battery, and then powering the phone back on