Bad audio in recorded messages

Hello All!
We use FreePBX (Asterisk 11.14.1 and FreePBX and we have the following problem:
When we record an audio message to be played for example when our office is closed the quality of audio in phone playback is very bad.
We respected all suggestions about audio data format but on computer the audio file is good but when uploaded on FreePBX and eared from phone the quality is really bad.
Have you any suggestion to solve this problem?

Thanks in advance and bye