You can mute a call while in a conversation to prevent the other party from hearing you.
Mute a Call
While in a call/conversation:
Press 
, or press [Mute], or the Mute keyboard key.
The Mute button in the Call Handling toolbar will turn red 
when Mute is enabled.
Unmute a Call
Press , or press [Mute] again, or the Mute keyboard key again.
Mute mode will be automatically disabled at the end of a call. For instance, when a call is cancelled or completed, the mute mode will be automatically turned off allowing for the Operators voice to be heard by the next incoming caller upon Answer.
If the Auto Unmute option is enabled, the console automatically unmutes when you perform an operation that connects you to another party.
For example:
When you mute a conversation with your connected party and dial another party who answers.
When you mute a conversation with your connected party and swap to another party by pressing [Source] or [Destination].
When you mute a conversation with your connected party and then form conference pressing [Conference].