Checking Phase Visually

images-phasePhase is simply one sound hitting two mics at slightly different times.  Phase issues usually are more apparent with drums, since there are several mics in use and lots of transients (loud peaks).
Sometimes it’s easy to hear phase issues, but sometimes it’s subtle but can really screw up a mix.
Here’s what I’ve been doing lately to check for phase on drums and it’s super-simple.
Get your drum kit mic’d up the way you like.  Could be 3 or more mics. Press record and have the drummer play for 10 seconds.
Then, zoom very close on all tracks (see image) and look for transient peaks.  If they are all going in the same direction, you are good to go. If they are opposite, you have a phase problem. In my studio, if I swtich the phase on the kick drum mic, it usually does the trick.  However, it will be totally unique to your setup.
You can also try moving a mic to alleviate the phase. Alternatively, you can shift the track in the session very slightly so that the peaks line up.
To help understand this, think about the distance the mic is from the kit.  The kick drum mic is very close usually, a few inches.  The overhead or room mic is probably a foot or more from the drums.  The sound is hitting the mic’s by milliseconds differently and that causes phase.
If you don’t have a phase switch on the mic-pre, you can switch phase by inserting a single-band EQ and click the phase button.
Experiment with it. You may find that killer mix just by testing for phase.