E-121 Phi is an E-Series robot that appears in Sonic Battle on the Gameboy Advance. Created by Dr. Eggman and based on the Gizoid research left behind by Eggman's grandfather Prof. Gerald Robotnik, Phi is also the only mass-produced model out of the E-100 line. It does not share the same body structure as the other E-100's and is physically modelled after the Gizoid robot Emerl. It possesses the same ability-copying technique that Emerl does, but does not possess the same level of power or intelligence. The Phi units are all powered by Chaos Emerald shards, rather than a whole Chaos Emerald like Emerl.