Phantom is a dark sorcerer who escaped the Kingdom of Star's most secure prison, and stormed his way to the castle in order to seize the Seven Holy Star Crystals -- however his plans were quickly foiled by Prince Yuko, as he sent the crystals to a location he wouldn't find. However, with extensive magic he was able to track the energy pulses of the crystals, and followed them to Earth. 

Not much is known about Phantom, those only know him has a deranged and crazy individual who wants to destroy the very fabric of space and time, and become God.