Hi @pbplus313058 ,

Try using the earphones with the microphone attachment and listen if you can hear OK when using them on a call.

If you can and since you can hear OK when using the loudspeaker then most likely there is a problem with the phone's receiver. It's either faulty or has come loose from the systemboard

Here is a link that shows how to replace the receiver in your phone.

Here is a link to some suppliers of the replacement part. It is not a recommendation to use them. It is shown to give an idea of the cost of the part.

If the repair process seems to daunting, I suggest that you contact a reputable, professional mobile phone repair service and ask for a quote to repair the phone.