iPhone 6 plus microphone issue

So using the apple supplied headset I can utilise all functions within my phone where the microphone is required but where using the phone on it's own I have issues with no audio in the video and am unable to utilise siri though apps like Music Memo and Voice Memo work fine as does Facetime. I have tried a reset but still have the same issue with the added bonus of "Voice Control" misinterpreting what I'm saying. I'm guessing that there has to be something wrong with the mic software in the phone given that it works in some apps but not in others. Any insight you can offer will be appreciated.