Phase Problem Detection Options

[evolution]

Hi

How do I detect phase problems in DP? or with a plugin? I am recording guitar with 2 mics (1 cond and 1 dyn) very close together about 40cms from neck and body join. I have clicked the phase reversal plug in one of the tracks on DP and sometimes the sound changes - my question is ... its great to have an easy fix but how do I know there is a phase problem in the first place? is there a meter/method that is in DP i can use? I examined the waves of the latest recording i did and on one track when the wave is up the wave on the second track is down - and when I pan them both to 12 oclock a lot of the bass and mid disappears - when i pan them apart the bass and mid reappears. So any ideas on easy phase problem detection?

Thanks!