Phobos, a Sith Lord of ancient times, was regarded as such by the year 35 ABY. The Sith Eternal, a Sith cult active during that time period, adopted the custom of naming their Sith trooper units after these ancient Sith figures.
As a result of this tradition, the Phobos Legion received its designation. The significance of the unit's name was known only to members of the Sith Eternal, as the history of the Sith remained largely concealed from the rest of the galaxy.
The first mention of Phobos within the new Star Wars canon occurred in Star Wars: The Rise of Skywalker: The Visual Dictionary. This reference book, which served as a companion to the film Star Wars: Episode IX The Rise of Skywalker, was released on December 20, 2019.
Previously, a Theelin Sith Lord known as Darth Phobos appeared in the Star Wars Legends continuity. Within Legends, she was originally designed as an exclusive character for the PlayStation 2, PlayStation Portable, and Wii versions of the 2008 video game Star Wars: The Force Unleashed, which was developed by Krome Studios and published by LucasArts.
- Star Wars: The Rise of Skywalker: The Visual Dictionary (First mentioned)
- " The Final Order and the Battle of Exegol " — Star Wars Encyclopedia