Phyllonorycter triarcha is a moth of the family Gracillariidae. It is known from India (Bihar), Indonesia (Moluccas), Malaysia (West Malaysia), the Philippines (Luzon, Negros) and Thailand. This species is a well-known pest of cotton.
The larvae feed on Gossypium species, including Gossypium barbadense and Gossypium herbaceum. They mine the leaves of their host plant.