Classification according to Bronsted theory :
 Â
H3PO4Â Â Â Â Â Â Â Â Â Â Â
+Â Â Â Â Â Â Â Â Â Â Â Â Â
C6H5O-Â Â Â Â Â Â Â <====>Â Â Â
H2PO4-Â Â Â Â Â Â Â Â Â
+Â Â Â Â Â Â Â Â Â Â Â Â Â Â
C6H5OH
   Â
acid                               Â
base                    Â
conjugate
base                Â
conjugate acid
So H2PO4- is the conjugate base of acid H3PO4 and C6H5OH is the
conjugate acid of base C6H5O- base. Â