Converts the prephenate produced from the shikimate-chorismate pathway into phenylalanine. H(+) + L-arogenate = CO2 + H2O + L-phenylalanine Amino-acid biosynthesis; L-phenylalanine biosynthesis; L-phenylalanine from L-arogenate: step 1/1. Expressed in roots, leaves, stems, flowers and siliques. More abundant in stems and roots. Strongly up-regulated during stem elongation. Has no detectable prehenate dehydratase activity.