The behavior of phenyl hydrogen α-hydroxyiminobenzylphosphonate (E)-2 in aqueous hydrochloric acid solution was examined by ³¹P NMR spectroscopy and by HPLC. Compound (E)-2 was found to undergo two competing acid-catalyzed reactions. 1) Fragmentation to phenyl phosphate (6) and benzonitrile, similar to the fragmentation of other hydroxyiminophosphonates to metaphosphate examined previously. The fragmentation of (E)-2 was found to be slower by a factor of 4 than that of hydrogen methyl α-hydroxyiminobenzylphosphonate ((E)-1). This phenomenon is interpreted in terms of inductive effects on the suggested metaphosphate intermediate. 2) Compound (E)-2 was found to undergo hydrolytic cleavage of the oxime group giving NH₂OH and hydrogen phenyl benzoylphosphonate (4), which was found to hydrolyze to phenol and benzoylphosphonic acid (5). The latter reacted with the NH₂OH liberated in the previous step to give α-hydroxyiminobenzylphosphonic acid ((E)-3), which fragmented to benzonitrile and phosphoric acid. The rate of a possible hydrolysis of the phenol group in oxime (E)-2 was shown to be slower by two orders of magnitude than that from ketone 4. This phenomenon is interpreted in terms of acid mediated retardation of acid catalyzed hydrolysis of phenol due to initial protonation of the oxime nitrogen in (E)-2.