In episode 61, when the fight goes on between Edward and Pride, Kimblee interferes with the mind of Pride. Edward uses this moment to attack Pride by getting into his mind (or body maybe). However, as this occurs, the dialog of Pride to Edward is this:

he turned himself into a philosopher's stone to infiltrate me?

What does this mean and how it is possible as Edward is not in possession of a philosopher's stone (not sure whether he can do it with a philosopher's stone)?