Vibrate On Ringer

Whether to vibrate on an incoming call.

You're probably really looking for the action Audio / Silent Mode if you want to put your phone in vibrate or silent mode.

Note: if silent/vibrate mode is engaged, this setting is overridden.

Note: if you are going to use Tasker for this, it's probably best not to mix it with other methods of controlling the setting.

See also: Ringer Volume.