The hydroxy group in a phenol molecule exhibits a strong activating effect on the benzene ring because it provides a ready source of electron density for the ring. This directing influence is so strong that you can often accomplish substitutions on phenols without the use of a catalyst.
Phenols react with halogens to yield mono-, di-, or tri-substituted products, depending on reaction conditions. For example, an aqueous bromine solution brominates all ortho and para positions on the ring.
Likewise, you can accomplish monobromination by running the reaction at extremely low temperatures in carbon disulfide solvent.
Hypochlorites can also induce electrophilic substitution reactions in substituted phenols or naphthols.