hI gUYS,,,The below mentioned steps worked fine for me,,,I believe it 's a frequent bug in Lumia devices(specialy the jack issue). Thanks alot
IF it will not help you out, u must go for the Jack replacement as its an internal speaker problem.
"Hey guys my name is Chris, I think I found a bug in my Nokia Lumia 928 device. I also found a solution
. Anyways
symptom : Internal speaker will stop working. When you make a call you can't hear anything but they will hear you just fine. Changing to loudspeaker you can hear everything just fine. Have not tries headphones or Bluetooth.
Cause: If you recently played music through 3.5mm jack and change settings under (Options>audio>) if you touch the the two settings DD or audio normalization. The next hours or day you will stop receiving audio from the front. Restarting the phone will not fix it, holding volume and power key won't fix it either.
Extra: Those two settings that I mention earlier should only be available if your phone is plugged via a 3.5mm however if you're experiencing this bug you can turn them off and on, even if those settings are suppose to be grey out because you are not connected to a 3.5mm cable.
Solution: plug the 3.5mm cable back again, go to audio settings and change the settings on and off. This time when you unplug the cable those settings should "grey out".
I had this issue more than once. The settings are under (Settings>Audio>enhancements)"