Without going into technical details (because I don't have a clue), I had a phase switch put into my dual humbucker guitar. When I switch it, the sound becomes more shrill, jangley, 'brilliant' sounding, but thinner. It's nice for cutting through a heavy mix, but tinny and too weak-but-harsh and jagged sounding on its own. Supposedly it puts the two pickups out of phase with each other, which in the case of my guitar, results in that kind of sound. My advice is to just listen to the difference in the sound. That's what it does. Let the electricians and mathemeticians worry about how it does it or why, I just worry about what it is good to use it for.