Watch the Phase After OD online guitar lesson by Jeff McErlain from Guitar Effects Survival Guide
To get an extreme phased sound we can put the phase shifter after our gain stage. If you are using amp gain, you'll need to put the pedal in the FX loop. When we do this the phase shifting becomes much more extreme and way less subtle, we end up hearing more of the effect than we do the guitar. This can be very cool in the right situation and where you wish to put this pedal in your chain is purely subjective, there is no wrong place. If you want a classic 70's style phase sound, place it before the OD.