Hi,
Check that the voice inlet hole on the bottom edge of the phone is not blocked with lint etc. (is the phone in a case that may be blocking it?)
''Do not'' use a pin or probe to try and clear it as you may damage the microphone that is located behind the hole.
Use a vacuum cleaner to try and suck out any debris that may be blocking the voice inlet hole
If still no good, try starting the phone in [https://motorola-global-portal.custhelp.com/app/answers/prod_answer_detail/a_id/156384/p/30,2670,4211|safe mode] and check if it works OK. If it does then a ''downloaded'' app is the cause of the problem The trick is to find out which one. A ''downloaded'' app is one that you downloaded and installed on the phone and wasn’t already pre-installed when you first got it.