Assertion (A): Given statement is correct because in phenol hydroxyl group cannot be replaced by halogen atom. Aryl halides cannot be prepared by replacing hydroxyl group of phenols because the carbon oxygen bond in phenols has a partial double bond character and is difficult to break being stronger than a single bond.
Reason (R):Phenols react with halogen acids violently. Aryl halides cannot be prepared by replacement of hydroxyl group of phenol by halogen atom.

Given reason is false
Hence Assertion (A) is correct but Reason (R) is incorrect.