IP Office Basic Edition - 1400 Series Phone User Guide R11.1Call Handling
While on a call, you can temporarily turn off the microphone so that the caller cannot hear you. You however will still be able to hear the caller.
To mute the microphone: (1403/1408/1416)
1.To mute the microphone, press the Mute key. While mute is active, the button is lit.