That is an interesting problem and I am not really sure that it is possible. Phthalic acid may not even be soluble in Phenol. Have you tried this?
Phenol has only one easily accessible functionality which is the hydroxyl group. to activate it, you would need an organic base like an alcoholic solution of KOH. Once the oxygen atom is activated, you might be able to tack on the Phthalate directly. Recovery might be done through crystallization in cold aliphatic naptha but I'm not 100% certain that this will work at all.

I found a synthesis using phthalic anhydride if that would help.

Whatever the answer, I think you have the wrong forum, and even the wrong site.