Enables phenylalanine 4-monooxygenase activity. Predicted to be involved in L-phenylalanine metabolic process; protein hydroxylation; and tyrosine biosynthetic process, by oxidation of phenylalanine. Predicted to act upstream of or within L-phenylalanine catabolic process. Is expressed in alimentary system; liver; and liver lobe. Used to study phenylketonuria. Human ortholog(s) of this gene implicated in intellectual disability and phenylketonuria. Orthologous to human PAH (phenylalanine hydroxylase). [provided by Alliance of Genome Resources, Apr 2022]