We present in this communication the preparation and the solid state NMR characterization of phenyl phosphonic acid encapsulated both in pure and aminopropyl-modified SBA-15 mesoporous silica materials. The 31P and 1H MAS studies revealed two radically different behaviors of the confined molecules. The included phosphonic acid in SBA-15 is submitted to a confinement effect that implies a weak interaction with the SiO2 surface and a relative mobility at room temperature. On the contrary, phenyl phosphonic acid molecules in the aminopropyl modified sample possess a strong interaction with the hybrid surface of the material. This finding is supported by a two dimensional double-quantum 1H experiment that revealed the close proximity between phenyl phosphonic acid and aminopropyl surface groups.