guiminer has phoenix as an available option. you were probably using the poclbm (OpenCL Miner), as I believe that is the default when using guiminer. if you continue using phoenix, I would recommend using the latest phatk kernel from this post http://bitcointalk.org/?topic=7964.0

cgminer has pretty comparable hash rates to phoenix. I haven't used diablo miner, but it seems to be fairly popular. check out the mining software board