A.T. Robertson Commentary Romans 2:28

"For he is not a Jew who is one outwardly; neither is that circumcision which is outward in the flesh:" — Romans 2:28 (ASV)

Which is one outwardly (ο εν τω φανερω). Ιουδαιος (Jew) has to be repeated (ellipse) with the article, "the in the open Jew" (circumcision, phylacteries, tithes, etc.). Likewise repeat περιτομη (circumcision).