diphosphate + N-(5-phospho-beta-D-ribosyl)anthranilate = 5-phospho-alpha-D-ribose 1-diphosphate + anthranilate Amino-acid biosynthesis; L-tryptophan biosynthesis; L-tryptophan from chorismate: step 2/5. Belongs to the anthranilate phosphoribosyltransferase family.