Historical Rules · 5 October 2018
Rule 107.4f
Official source text from the 5 October 2018 Rules release
Phyrexian mana symbols are colored mana symbols: {W/P} is white, {U/P} is blue, {B/P} is black, {R/P} is red, and {G/P} is green. A Phyrexian mana symbol represents a cost that can be paid either with one mana of its color or by paying 2 life. Example: {W/P}{W/P} can be paid by spending {W}{W}, by spending {W} and paying 2 life, or by paying 4 life.