Can't hear the caller on Moto E I have a Moto E with kitkat 4.4.4.
I can not hear the caller's voice unless I put my phone on speaker. 
noticed this problem yesterday only.. earlier it was working fine.
Will appreciate any help regarding the issue.
I had the same problem and this solved it.

1.With the phone powered off, press the VOL DOWN KEY for 2-3 seconds, then POWER key, then release.

2.The device will display different BOOT OPTIONS
Use the VOL DOWN Key to SCROLL to Recovery and VOL UP Key to select

Tip: If the device reboots, you may have waited too long to make a selection, you will need to begin the process again. 
The device will display the Motorola logo and then the Android in distress (logo with Exclamation mark)
Press and hold the VOL UP key for 10-15 seconds. While still holding the VOL UP key tap and release the POWER key

Tip: You can try this step, holding the phone in landscape. If you are stuck on step 6, try a force reboot by pressing the POWER key and VOL DOWN key, and start the process again.
The device will display additional menu options (Text will appear in BLUE) 
Use the VOL DOWN Key to scroll to wipe cache partition and the POWER Key to select this option
The device will then perform the partition wipe
The device will reboot and start the normal power up sequence

DISCLAIMER : I am not responsible for any loss of data due to you doing any of the steps wrong. follow the procedure. It should work out well.

Good Luck!