[Punkest]

no harm intended, but if you got your main speakers out of phase and you don't notice, you are not listening...
the most important thing in music and recording is to listen, and pay atention to what your ears tell you... then you can take advantage of many things, even phase issues...
even a recording done with just ONE mic can have phasing if placed near a reflective surface, due to comb filtering.
i love to place many mics in front of the gtr. amp. and mix the signals using phase as a form of sculpting the sound, specially when trying to get a grunchy distorted kind of sound. other thing that works for me, is to crank up mostly the best sounding mic of the session without eq, and then if i need more high or low end, you dramatically boost one of the other mic's signals with eq, and mix to the amount desired to the other signal. I feel that the obtained sound i get is more natural that when you apply eq. to the whole thing. I kinda feel that eq, breaks the distorted gtr. sound a bit. When you are not shure about the sound, maybe because you are not in your place and you don't feel confident about the monitoring, you can record on multiple tracks each of the mic's signals and live the final sound for the mix.
Knowing your monitors is crucial. 
as many allready said, if the phase is causing severe cancellation, you don't need a plug in to hear it, but if you are looking for a thin wierd sound (which can be the case depending of what you want for the song) then the sever phasing is there to help you. A small amount of phasing can color the sound in pleasant and uncommon ways. Use the best plug in you got, wich is plugged to your head: EARS.
Hope this helps