Catalyzes the Claisen rearrangement of chorismate to prephenate and the decarboxylation/dehydration of prephenate to phenylpyruvate. chorismate = prephenate H(+) + prephenate = 3-phenylpyruvate + CO2 + H2O Amino-acid biosynthesis; L-phenylalanine biosynthesis; phenylpyruvate from prephenate: step 1/1. Metabolic intermediate biosynthesis; prephenate biosynthesis; prephenate from chorismate: step 1/1. The regulatory domain shows changes in the ESRP sequence, which is involved in the allosteric binding of phenylalanine. These changes suggest the desensitization of the enzyme to inhibition by phenylalanine and would permit the overproduction of phenylalanine.