Empress Effects Phaser - Manual (Page 11)

Submode 8: Direct Control Mode
Without an expression pedal plugged in to the control port,
this mode operates like submode 5, except that it triggers
only when you hit the tap stomp switch. Hold down the tap
switch and the sweep will keep rising to its maximum
value. Release the tap switch and the sweep will return to
its starting value.
If you plug an expression pedal into the control port, this
submode will allow you to control the degree of phase
shift with the expression pedal. The speed knob, width
knob, and expression switch are ignored in this mode.