The "Phoenix" is a non-aggressive boss in Dreamscape. It is one of the more popular bosses due to its ultra-rare drop - the phoenix eggling, which provides 10% extra drop rate.
At Phoenix, there is no doubt you want at least a "Fast-Hitting" weapon. There are four monsters that you have to kill. The three minions, and the actual Phoenix. Phoenix is not really hard to kill. It just has a lot of HP. So be prepared to stay there a while if you do not have a "Fast-Hitting" weapon. Also, it is highly recommended that you pray "Soulsplit" (Level 92 required) and "Turmoil" (Level 95 required).