Magnetic nanomaterials with the desirable nature are the basis for developing future spintronic devices, and research for them is of fundamental interest. Here, we explore the realization of half-metallicity and magnetic phase transition for phagraphene nanoribbons in virtue of functional groups (OH and CN) with different coverage fractions and external electric fields. The first-principles calculations show that a single-edge CN functionalization only makes a intrinsic spin-degenerate semiconducting ribbon converted to a quasi-metal or metal, ...