Here is what the EP600/EP500 manual has to say about phase. Coincidentally, I JUST HAPPENED to be perusing the manual today.

0 & 180 PHASE: This synchronizes the in/out movement of the subwoofer
cone driver with the other speakers in your system. Once you have
chosen the best location for your subwoofer, try flipping the phase switch
between 0 and 180 to see if one or the other setting produces deeper and
smoother bass output in your room. Leave the switch at the setting that
results in the smoothest and deepest bass at several listening locations
in the room. If you hear no difference, leave the switch at the 0 position.
Quite often the phase switch makes no difference, but it’s dependent on
your room and subwoofer location."

(bold emphasis is mine.)

Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton