Hello Satya

Phenol and benzoic acid can be distinguished easily with the help of ferric chloride test.

In Ferric chloride test, phenol reacts with neutral FeCl 3 to form an iron-phenol complex giving violet colouration. But benzoic acid reacts with neutral FeCl3 to give a buff coloured ppt.

So ,it's clear now that if phenol gives violet colour with Fecl3 whereas benzoic acid reacts with  FeCl3 to give a buff coloured ppt . So, on the basis of colour they give you can easily identify and distinguish between them.

I hope that it helps you

Thankyou