The catalytic performance of an unsupported Ni₂P in the aqueous phase hydrodeoxygenation (HDO) of phenol was investigated. It was found that the unsupported Ni₂P was water-sensitive, being transformed stepwise, first to an amorphous phase and then to Ni₅P₂ and Ni₁₂P₅, and finally to Ni₃P in the presence of water at elevated temperatures. Nonetheless, the generated Ni₃P phase exhibited extraordinary hydrogenation activity at low temperatures and high HDO activity at high temperatures. The unsupported Ni₃P was more active for the hydrogenation of the aromatic ring in the phenol molecule than Pd/SiO₂ (1.0 wt%). The unsupported Ni₃P was catalytically active and stable in phenol HDO in both the aqueous phase and the organic phase. In addition to phenol, catechol and o-cresol were investigated in the HDO catalyzed by the unsupported Ni₃P in both aqueous solution and decalin solution. The HDO reactivity decreased in the order of phenol > catechol > o-cresol in the aqueous phase, and in the order of phenol > o-cresol in the organic phase (catechol is insoluble in decalin). In the oil phase HDOs of phenol and o-cresol, the unsupported Ni₃P exhibited superior hydrogenation activity to that of the unsupported Ni₂P at low temperatures.