Mute phone's microphone during call other than on call status screen

[speck]

I know you can mute the phone ring by flipping the phone over.

Is there any kind of hack that will mute my voice during a call when I flip the phone over?

I'm on a lot of (long) conference calls where I'm using the speaker. Using the screen button to mute is a problem, because my screen is usually off. It would be great to just flip the phone to mute and unmute.

(P.S. I did search, but I could only find threads about muting the ringer.)