Designing excellent electrode materials by establishing superb architectures provides a feasible way to boost the electrochemical properties of supercapacitors (SCs). Herein, a self-supported bimetallic Ni-Fe phosphide (Ni-Fe-P) electrode with a newfangled and multidimensional construction was synthesized by a two-step process. This electrode consists of connective nanosheets which combined numerous interlinked nanoparticles with well-distributed mesopores. By investigating the effects of phosphating temperatures, an optimal phosphide electrode with well-distributed pores throughout the interlaced nanosheets has been obtained. Due to this sophisticated porous structure and the mechanical stability enhanced by the direct growth on binderless Ni foam, the Ni-Fe-P electrode exhibits outstanding electrochemical performance. Density functional theory (DFT) calculations are also performed to demonstrate the increased electrical conductivity and reactivity after the introduction of Fe atoms and phosphorization. Impressively, the fabricated Ni-Fe-P//reduced graphene oxide solid-state SC device delivers an outstanding energy density of 50.2 W h kg-1 at a power density of 800 W kg-1, and remarkable cycle performance (91.5% retention rate after 10000 cycles). This comprehensive work not only displays a new perspective of the phosphating mechanism at different temperatures but also suggests a versatile approach for engineering promising electrode materials for advanced SCs.