give reason for the formation of tribromophenol when phenol is treated with aq.bromine

In phenol there is -OH group present in benzene ring.This -OH group makes phenol much more reactive than benzene.
When phenol is treated with bromine water,it decolourises it and resulting in the formation of white colour ppt.of 2,4,6-tribromophenol.Trisubstitution takes place without the presence of any Lewis acid like in benzene.It is because one of the lone pairs of electrons on the oxygen atom in -OH group overlaps with the delocalised ring electron system,as a result of which e- density around the ring gets increased.Due to this the ring becomes more attractive towards incoming elctrophiles.So multiple substitution occurs in phenol on treating with bromine water.
C6H5OH + Br2(aq.) ------------------> 2,4,6-tribromophenol