In this paper, I argue that Xuansha Shibei's (玄沙師備) Theory of The Three Phrases (sanjugangzong 三句綱宗), which is a variation Baizhang Huaihai's (百丈懷海) Theory of The Three Phrases, is representative of his doctrinal system. In this theory, enlightenment deepens through three stages (or phrases): the first, second, and third phrase. With the first phrase, Xuansha argues that we come to know Buddha Nature — which exists inside of our minds — through cognition. With the second phrase, we find that Buddha Nature actually exists on a level different from that of cognitive activity. In the third and final phrase, we come to see that Buddha Nature permeates the phenomenal world. As I will show, this theory was formed against the background of Chan (Zen) teachings in the Tang dynasty.