Module A-125 (VC Phaser) is a voltage controlled phase shifter.
Phase shifting can be controlled either manually or by voltage control.
Other parameters which can be controlled are resonance (governing the depth of the comb filtering, and tonal color) and mix (the amount of the original signal which is added to the phase-shifted signal). The A-125 is used to generate the typical phaser sound ("jet sound"). Due to the voltage control feature not only the usual LFO-controlled phasings but even ADSR-, random-, sequencer- or S&H-controlled phasings are possible. In combination with the Shepard generator A-191 and several A-125 never ending barberpole phasing effects come true.

For more detailed information please look at the English user's manual A125_man.pdf

Below you will find the frequency response of the A-125 for different phase shift settings.

A similar module is the modular 12 stage vactrol phaser A-101-3.