Bluetooth issues only when making calls

My iPhone 5 Bluetooth works fine except when making a call. The line rings static/distorted and when someone is talking it is just static/distortion. I have reverted to an older iOS 8.2 to 8.3.1 and the issue is still present. Happens on all Bluetooth devices I have, hands free car, Motorola headset, etc. I can't figure out if the Bluetooth unit went bad in the phone or software/iOS is responsible?