Nephon I of Constantinople (Niphon of Cyzicus; Greek: Νήφων; died on 3 September 1328) was the Ecumenical Patriarch of Constantinople from 1310 to 1314. From Veria, Greece. Nicephorus Gregoras claimed Nephon to be illiterate, a lover of luxury, and ill-suited for the position. Due to his willingness to compromise, during his time as patriarch the Arsenite Schism was healed within the Byzantine Church. Nephon I abdicated the throne after four years.

Nephon I founded the Church of the Holy Apostles in Thessaloniki and his ktetor portrait exists at the church walls.