Who can do this? Call owners who have the ability to set calls as private enabled in their permission profile.
Set calls you own as private to restrict access when the conversation covers sensitive subjects. This action can be done before or after the call.
By default, a private call can only be seen by the call owner and any other internal participants on the call. You can give access to additional people by sharing the call either internally or externally.
Regardless of the privacy setting, all calls are used in statistics and calculations, e.g. in Stats and Deal warnings, and the existence of private calls is visible to everyone on all pages. People without access can see that the call occurred, see who the owner is, and see the date and time of the call.