Phone mute
 

I have a 2010 RA with the factory NAV and bluetooth for connecting with a cell phone. What is annoying me is that when I want to mute a phone conversation (to save the rest of the people on my call from the noise) I have to use my phone's mute function or the voice command to the Mutibishi system which is a extremely slow.
Does anyone have a more convenient method for mute?