COOH is a bulky group. and any group at ortho position causes steric hinderence. due to this the planarity of COOH is lost.

We know that for resonanace the molecules under consideration shod be planar. ther4 resonance is inhibited.

U can easily see that Ph stabilises COOH by resonance.(in the canonical structures u can see that -ve charge comes on 1 O.

think if H is released(rather H+) it brings -ve on he other O also.

and it leads to a large repulsiv force(between 2 O-.) ther4 release of H+ is now prohibited

 

BUT when, planarity is lost i.e resonance is stopped. ad now -ve not comes on any O. and elease of H is facilitated.

 

 

I think now u ll hv no confusion..................