Newbie question about reversing Phase??

That's all you have to do. Just be sure your amp doesn't reverse phase as well (if it does, you don't have to do anything).

I don't know why but every product,whether amp or pre says; do the reversing at the speaker.--I have an amp in one system and a pre in a different system that do this.--Each manual says do it at the speaker terminal.

Newbie:
There is something called "absolute phase". If a single speaker is wired out of phase, it's initial excursion is back, not forward. You can feel this by putting your finger on the speaker cone and feel if it pushes out or in when, for instance, a bass drum kicks. All the speakers can be in phase with each other but the whole system can be 180 degrees out of phase in reference to the original recording. Even a turntable cartrige can be wired out of phase and screw everything up from the start.
So begin with a single speaker and make sure it's not 180 degrees out of phase and reference the other speakers to it. Also some speakers can be mismarked at the terminals. A simple test is to take a 9 volt transister battery and, using a test lead with aligater clips, connect the positive of the battery to the positive of the speaker. With your finger on the diaphragm, feel the excursion as you touch the negative aligater clip to the negative lead on the speaker. If it is correctly wired the diaphragm will push out when you touch the terminal with the aligater clip. This will tell you if positive is really positive with respect to the internal speaker wiring. To be sure, test all the speakers in our system. Finally, rocket science explained!