It sounds like you want it to as powerful as possible, at least that's what I think when I hear the word deep when pertaining to phasers. The most gnarly phaser I've played with yet is the Pigtronix EP2, it's NASTY. Unlike the gentle and most loved MXR Phase 90 (which is probably the most usable phaser I've messed with), the Pig's low end sweep is the most massive I've heard yet. It's got an envelope mode and LFO, both of which take some messing around with due to how outta control this jamma can get on you in a hurry.