I dont' quite remember what you're referring to Dark Phoenix. What evil thing is it that he does? Aside from that, he's actually probably the best character to have in your party. His stats outnumber every character in every category except for strength (usually Crono and he are close, and Ayla and Robo are higher) and agility (usually really close to Crono, and Ayla is higher). Not only that, but his higher level spells are some of the most powerful attacks in the game.