Phosphophyllite  is the main protagonist and the youngest Gem when the story began. They're weak, brittle - not suited for battle - and their clumsiness makes them difficult to maintain any other roles. Phos has always wanted to be useful.

Phos' initial job was to make a natural history encyclopedia which they progressed very little on. They promised to help Cinnabar find a job suited for them as well.

Phos so far is the only Gem who has had drastic body and personality changes.