Creatine phosphate is used as a buffer in high energy using cells, such as muscles. In a cell you have a pool of ATP, which is needed for things like muscle contraction, and then you have your pool of creatine phosphate, which can not directly be used as energy for muscle contraction. The cell only stores so much energy as ATP. And during high energy activities it can be depleted quite fast. The problem is that it takes a lot of time to make ATP through oxidative phosphorylation. And while glycolysis is faster, you dont get nearly as much ATP. Creatine phosphate solves this problem by acting as a reserve of ATP, so when ATP is depleted, the creatine phosphate can transfer a phosphate to ADP, and thus restoring ATP without needing to wait for glycolysis or the electron transport chain to complete.