We describe a new class of inorganic polymeric materials featuring a main chain consisting of P-v-O bonds and aryl side groups, which was obtained with >70 repeat units by ring-opening polymerization of cyclic phosphonates. This monomer polymer system was found to be dynamic in solution enabling selective depolymerization under dilute conditions, which can be tuned by varying the substituents. The polymers show high thermal stability to weight loss and can be easily fabricated into self-standing thin films. Structural characterizations of the cyclic 6- and 12-membered ring precursors are also described.