The dioxaphospho-lane ring in the title compound, C(20)H(17)O(3)P, adopts an envelope conformation about one of the ring carbons. The benzene rings of the compound do not form face-to-face π-π inter-actions, instead weak C-H⋯π inter-actions occur between adjacent mol-ecules. The methine H atoms on the dioxaphospho-lane ring form weak C-H⋯O hydrogen bonds to the oxide group of an adjacent mol-ecule.