ARF Phase I armor served as the standard armor for Advanced Recon Force Scout Troopers, who were specialized clone troopers within the Grand Army of the Republic. The Phase II ARF armor eventually superseded it.
The design for an Advanced Recon Force Scout Trooper, which was initially unnamed, was first seen in Star Wars: The Clone Wars film and this design was the Phase I ARF armor. Its official designation as Phase I ARF armor was later confirmed in a post on the Star Wars Battlefront II website.