Yes, this is normal.
What's going on during a phase test is you are making sure all of your speakers are moving in the same direction at the same time.
The classic phase test is with two stereo speakers. If you play mono music on a stereo with everything hooked up correctly, you'd hear the sound come out between the speakers. If you could see really fast, you'd find your speakers are moving together. The two woofers are moving in and out at the same time.(Or, if you were a college kid back in the 1970's who had a technical bend, you'd take some chalk and draw rings on your speaker's woofer. That way when your strobe light went off in your dorm room, you'd get a snapshot of the woofer moving. Bitchin'.)
Now reverse the wires to just one speaker so that the hot wire goes to the black terminal on the speaker and the negative wire goes to the red one. When you play the music, it now sounds like it's coming from each speaker, not the middle, and all the bass has gone away. A slow motion camera - or a stoned hippie - would see the woofers moving opposite of each other. They are cancelling each other's bass.
You'll find phase switches on the back of subwoofers. Clicking it back and forth makes sure all your front speakers are pushing and pulling together. In one position, the subwoofer cancels some of the bass coming from the mains. In the other position, it re-enforces the bass. You want the position that gives you the most bass. You may have to listen over the course of a night to hear the difference but it's there.
When you are doing a phase test on your home theater system, the microphone that came with your receiver is measuring whether this is happening with all the speakers in your system. Are they all reinforcing each other? The speed of sound comes into play as sound moves about a foot every milisecond, so it's more complicated. That's why God invented microprocessors, although I've been listening to get the phase right for years. You can do it by ear.
You will find no matter what your system tries to do, there will still be areas in your room with more bass and others with less. That's the nature of rooms. But overall, you should get more bass when the phase is set correctly.
EDIT: I should have known half a dozen other posters would beat me to the punch if I wrote a long reply!