Phase affects just about everything that touches audio. It's something you really have to hear to be able to identify. An interesting tip I learned recently was that if you know something has wacky phase, become allergic to that sound.
When using a spaced pair or similar (drums, multiple mics) for capturing a source, your chain should have a "phase" control somewhere on it. Circle with a slash through it. A lot of preamps and some direct boxes and other such gear have this on each channel as well as many audio interfaces. If not, there should be one in your DAW channel if you're recording to a computer. Listening to both mics in mono, you can flip the phase of one of the mics. These controls work as a polarity invert, so the phase will either be 0 degrees or 180 degrees.
If one position sounds more or less full, or just gels better or something, it doesn't really matter where you leave the control. It's easy to hear a drop in low end when things are out of phase. If you were to use a coincident mic technique like x/y, you'd want to leave both channels at 0 degrees. Flipping one of the channels should be a good demo of what "out of phase" sounds like on many sources. A strat in the "out of phase" position is another.
If you're getting good sounds I wouldn't get too hung up on phase. It's worthwhile to do a quick check and learn what you're listening for, especially when recording drums. Depending on the relative distances of the mics to the source and each other, sometimes very small movements of one of the mics will change the tone quite a lot as the phase relationship changes. The best thing in that scenario is to monitor the signal from a remote location and have an assistant move the mics until it sounds right. The idea isn't to get the phase perfect so much as good. Perfect phase isn't possible a lot of the time anyway. Moving the mics is the best way to tweak it. As the mics get closer to each other relative to the source, the phase interaction gets wackier.
Again, using a coincident mic technique like x/y is a good way to not have to worry about phase, but there are merits to other techniques. It's subjective. Comes down to what you like.