John321V, that would certainly become annoying while on a call. Let's help keep the conversation flowing.
Does this occur during every call?
Any recent updates to App or your OS prior to these issues starting?
Do you currently have a passcode set up on your phone for when your iPhone is locked?
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To answer your questions :
My Iphone 6 does not mute on every call, just some calls
I always update phone when updates are available and I recently updated to IOS 9-2
I do have a password set up on my phone when it is locked