Assertion (A) : In the bromination of phenol in CS₂, a Lewis acid is not required.
Reason (R) : In this reaction phenol it self acts as Lewis acid.

During the bromination of any non polar substance like benzene, Lewis acid is used to polarize the attacking electrophile Br₂​.

But in case of highly polar phenol molecule, the oxygen atom present in the phenol molecule itself polarizes the incoming electrophile Br_2​ to form ions. SO in this case no additional Lewis acid is required.