Why can't I hear callers after installing new upgrade? I was notified on my phone that it had an upgrade so I selected it. Now no-one can hear me unless I put it on loudspeaker although I can hear them?
There is no guarantee, but hard reset most time tends to fix this type of problems, try and observe your phone closely, you might have some apps that might be manipulating the speaker in your phone. Take time to troubleshoot the problem. 

If there's no app causing the problem, then you can run a Factory resetting for your device by following the steps, 


  
  click on your menu list
  Settings
  Backup and reset 
  click Factory data reset which usually should be at the end.
  Reset phone or Reset device. 
  


Ensure you have adequate charge on your battery to handle the entire process and that battery is not mistakenly pulled off during the process, because if any happens, it can lead to corrupting of data.