Problem: What do you do when you must temporarily leave the call for personal or work reasons?

Recommendation: When you have to leave the call for a moment it is best to tell the others you will be gone. It is tempting to sneak away in silence and hope they will not notice your absence, but there is always the chance they will ask you a direct question and your silence might be misinterpreted as either withholding or a certain lack of alertness.

From: http://www.conferencecallogy.com/Conference-Calling.html