Hello, do you mean a "mute" button? There is one on the side of the page. Press it once and you are muted in the call, press it again and you can talk again or you can be heard. If that's what you mean... And otherwise the previous answers.

The microphone cannot be switched off on the unit itself; this must be done via the programme that is being used.

The mic cannot be switched off in the hardware. However, this can usually be set in the software (e.g. Teams or Zoom, as well as in the phone application).