Q: IPHONE4 CANNOT HEAR CALLER ON PHONE. MUST USE SPEAKER PHONE

Hey MAMPOLING,

I understand that you can't hear people from the receiver on your iPhone 4. Let's go over some troubleshooting options to get you back up and running. 

The things to check for is the volume for when you are on a call and check to see if you are connected to Bluetooth device. I would also look at the receiver itself to see if it clear of any debris. Take a look at the article below for more details to sort this out. 

If you can‘t hear a person on a call or voicemail or if the sound isn‘t clear on your iPhone
https://support.apple.com/en-us/HT203800

Take it easy