Just like the color filter has a colorless option, I think it need a Phyrexian option, but not 5 more options. This way as I'm deck building I could filter on "One of : White, Blue, Phyrexian" and it would return all my white cards, blue cards, and any color phyrexian cards. Alternatevily I could search for "All of: Red, Phyrexian" and get just the Phyrexian Red cards.

I can see why this would be a good idea, but the Magic definition of color as present in the comprehensive rules does not account for the phyrexian mana. Colors are clearly stated as red, blue, green, black, white and colorless. I would rather stick to this definition, one single set does not justify a new filter.

For now, selecting New Phyrexia as the edition, and your target color should reduce the options to less than one page anyway. If phyrexian mana becomes a larger theme we might address it another way in the future, just not with the color filter.