Stereophile test CD2 In/Out of Phase test:question

Absolute phase is not recogonized by everyone. I used to not be very sensitive to it, and would still say that I'm less sensitive to it than some of my colleges. I do find that it's pretty apparant with solo upright bass. Piano works well too--but not quite as good as bass. Our test CD has phase testing, but goes through inverting individual channels and then both channels.

That test shows whether your speakers are in phase with each other, it doesn't show absolute phase. That means if they are being fed the same signal the cones will be moving in and out together. If the phase is reversed then when one speaker is moving in the other is moving out.

If your speakers are in phase, and you reverse both speaker cables at the same time, they are still in phase. You just reversed the polarity.

FYI, the correct term is really polarity, but phase is used so often it has come to be accepted as being correct.
Phase has to do with time.
Polarity has to do with whether the signal is positive or negative, or in the case of a speaker, whether it is moving in or out.

If two signals reach their peaks at the same time they are said to be in phase. If one signal reaches it's peak earlier or later in time than the other then they are out of phase. If you switch the leads on your speakers you haven't changed any timing, you have reversed the polarity.

The test is for absolute phase or polarity not for one speaker being out of phase with the other. Only careless installation would have that happen.

Changing the leads at the amp or at the speaker equally deal with change the absolute phase.

Remember, however, that many recording are recorded out of phase and some with some microphone in phase and others out of phase.

Some preamps provide a phase switch, although many add another stage to do so, which hurts more than it helps.