Difference between polarity and phase w/sub

I had the same questions about phase control on a sub.  Most have them.  With the vast majority this is best put as phase "at 80 hz".  It's implementation is a simple time delay, milliseconds.  For example, 180 degrees reversal is really an "equivalent" done with  time delay such that 80hz is fully out of of phase with the main since the half wavelength in time of 80hz can be defined by time.  Around 32ms.  Set to 90deg and it's really a 16ms delay.  Effectively 90deg at 80 hz but now fully out at 160hz.  The good news is that subs have low pass cutoffs and often slopes to play with.  Personally I'd start at 90deg so that mains to sub handoff isn't boosted with a bloom nor suck-out at most affected/audible overlap area or... 80hz.   Vary from there to match room/sitting position.  The knob exists to control bloom/suck-out.  Setting to "most bass'" may just be bloom or room node.