The optical excitations in layered phosphorene oxides are studied via ab initio calculation together with GW approximation for the self-energy and solving the Bethe-Salpeter equation (BSE) for the excitations. It is found that the electronic structure of phosphorene oxides closely depends on the oxygen concentration. For the high oxygen coverage structure P4O10, it shows a strong localized molecular-like electronic structure with exciton binding (E-b) energy up to 3.0 eV, which is several times larger than the ordinary E-b value in various low-dimensional materials. This study may provide an alternative way to design functional layered materials with large exciton binding energies by controlling the oxidation level in phosphorene oxides.