17O-enriched phenylphosphonic acid (PhP*O3H2) was prepared from phosphonic acid dichloride and enriched water. This enriched phosphonic acid was used to prepare the titanium oxo-alkoxo-phosphonate Ti4(í3-*O)(í2-OPri)3(OPri)5(PhP*O3)3 (1) as a model compound, and titanium oxide/phenylphosphonate hybrids either by sol-gel processing with Ti(OPri)4 or by surface modification of a titania support. For comparison a gel sample was prepared using nonenriched PhPO3H2 and enriched water. The 17O MAS NMR spectra of these 5 solids have been recorded at various magnetic fields (7, 9.4, and 17.6 T) and the isotropic chemical shifts and quadrupolar constants have been determined for the different oxygen sites: PdO, P-O-H, P-O-Ti, and OTix. These spectra give direct evidence for the presence of extensive Ti-O-P bonding in the hybrid materials.