Catalyzes the reversible NAD(+)-dependent oxidative deamination of L-phenylalanine to phenylpyruvate. Is also able to act on L-tyrosine, but with 100-fold lower efficiency. H2O + L-phenylalanine + NAD(+) = 3-phenylpyruvate + H(+) + NADH + NH4(+) kcat is 50 sec(-1) with L-phenylalanine as substrate. kcat is 58 sec(-1) with L-tyrosine as substrate. Amino-acid biosynthesis; L-phenylalanine biosynthesis; L-phenylalanine from phenylpyruvate (PDH route): step 1/1. Phenylalanine dehydrogenase (PheDH) is a key enzyme in medical diagnostic for determining the amount of phenylalanine to detect phenylketonuria (PKU) disease. The mutant V144L has a higher specificity for phenylalanine substrate and may provide a suitable candidate to increase the specificity of PKU detection in clinic. Belongs to the Glu/Leu/Phe/Val dehydrogenases family.