After replacing iPhone 4S screen, I cannot hear phone calls

Hi Paul,

I know it'll be inconvenient, but you may want to check for any loose cables inside the iPhone. IIRC Correctly, Sound Recorder and Voice Memos uses the top microphone as well as the bottom one which is why you will be able to hear yourself in a recording, but phone calls use just the bottom one for voice, and the top one is uses for noise cancelling using the Audience chip, so the person on the receiving end won't be able to hear you.

Also, there may be a loose connector for the earpiece speaker.

Following this guide, remove the front assembly, making sure to pay attention to the ribbon cables and not to damage them (Yes this might seem counter productive, but it's for the best! (Fixed iPhone!)). Then, check the connection of all the cables, and replace the assembly. (Follow that guide in reverse)

Then, do a test call with a friend to make sure the problem is resolved.

Hope this helps get your iPhone 4S back in shape!!

-Chris P