Elapsam semel occasionem non ipse potest Iuppiter reprehendere.
Phi is a light-skinned, blue-eyed girl with short white hair topped off with a large black flower. She wears a white shirt over a short black dress that has a sky blue design along the bottom. She also wears a long, sleeveless jacket with the same sky blue color. She has black necklaces that she wears over her shirt and large, shin-high black boots.
Phi has a distinctly cold personality and only rarely reveals her compassion. Small quirks of Sigma's like his counting down before opening a door manage to piss her off, and she never seems to particularly like anyone. Phi has a dry sense of humor but nevertheless pursues it in her conversations with Sigma. Phi is immensely intelligent and infrequently allows her emotions to control her. She is always the one to plan out how the chromatic doors will work, which shows her leadership as well. Phi uses rational logic to come to decisions especially during the AB games. Though she seems to be heartless, she would never use the game to kill anyone, and she wants to escape with everyone. She even softens up at times like when thanking Sigma for being there for her or talking about Quark in certain timelines.
By the end of the game, the player knows the least about Phi. She never explains her occupation as many of the other participants do. We know that Phi was born around 2008, two years after Sigma and a year before Clover, but anything else about who she is remains a mystery for now.
Zero III calls her "Phido" because, when she was a child, her parents had sung a modified version of "bingo", where they instead sung "P-H-I-D-O" rather than "B-I-N-G-O".