From what I understand, Peter Green put his neck pickup in back to front - the screws were towards the bridge instead of toward the neck - effectively putting the neck pickup out of phase with the bridge pickup. This can also be achieved by retaining the screw position but reversing the polarity of the magnet or by reversing the direction of the coil winding. A phase switch does the latter although it can affect the humbucking effect in single pole pickups. I have never had a problem with that as I screen my cavities.
no, this is not correct.
rotating the pickups 180 degrees like Peter Green did does not change the phase - think about it, the wire is still in either a clockwise or anticlockwise direction, and the magnets are still pointing in the same direction towards the strings. Rotating the pickup will make the sound slightly brighter though since the screw pieces are higher than the slugs and they now nearer the bridge.
to change the phase you have to adjust the magnet, or the wind direction, or a phase reversal switch. all these three options will reverse the phase, but they do so in a different way.
edit: also, if you use a phase reversal switch on humbucker, make sure that you have multi conductor wiring on that pickup or you will have grounding issues.
