Appearing only in the manga and musicals, Sailor Phi, together with Sailor Chi, may be Galaxia's most loyal servants. She is named for one of the letters of the Greek alphabet, which is written Φ (Phi).

The two have similar outfits; Chi's is green, bares her midriff, and ends in a long skirt slit to the thighs. Phi's is red, covers her midriff, and ends in pants. Each carries a staff with a sun symbol on top of it, which they can use to fight. Sailor Phi also uses an attack called Galactica Plants Blizzard.

The pair are known as the Starseed Gardeners, or the Garden Crystal Senshi, and watch over the starseeds that are kept in the gardens around Galaxia's palace. They serve as messengers for Galaxia, overseeing her other servants and reporting on their actions. Sailor Phi first appears in Act 45, reporting Sailor Aluminum Siren's failure. Sailor Chi appears later, in Act 48. Sailor Chi and Sailor Phi are responsible for the deaths of all three Sailor Starlights, Princess Kakyuu, and probably many others. They are defeated by Eternal Sailor Moon in Act 49, but not before they greatly increase Sailor Galaxia's power.