Bad outgoing call quality. What Mic or Colder joint is broken? iPhone5

Hope somebody might be able to help.

My outgoing audio Signal on phone calls is very bad since a few month.

(Somehow the signal is way better(but still crappy) when holding the phone on my right hand instead on my left hand)

Recording Audio in Videomode or as Voice recording is fine. The network connecting is alright as when I use a external mic the problem does not occur.

I exchanged the following parts. (Dock Connector, Audio Jack, Flex Antenne, Mic and The ambient microphone)

I cleaned the little holes on the bottom of the phone of any dust and dirty.

And... I have no idea what the problem might be causing.