CoFe layered double hydroxide (LDH) has emerged as a promising oxygen evolution reaction (OER) electrocatalyst but exhibits low intrinsic activity and instability at high current densities, limiting industrial applicability. Herein, a phase-engineering strategy is reported to derive highly crystalline phase-transformed hexagonal Fe-Co<sub>3</sub>O<sub>4</sub> (PH-FCO) via selenization of CoFe LDH to form Fe-Co<sub>0.85</sub>Se, followed by electrochemical activation. Selective Se leaching during activation induces a morphological transition from needle-like Fe-Co<sub>0.85</sub>Se to hexagonal PH-FCO. The resulting PH-FCO achieves a high current density of 2 A cm<sup>-2</sup> and maintains stability for over 300 h at 500 mA cm<sup>-2</sup> and 1 A cm<sup>-2</sup>. Enhanced crystallinity formed during phase transformation effectively suppresses dissolution and preserves active catalytic sites. First-principles density functional theory calculations reveal that Fe incorporation promotes lattice oxygen oxidation, improves electronic conductivity, and reduces energy barriers. An anion exchange membrane water electrolyzer (AEMWE) incorporating PH-FCO as the anode and NiMo alloy as the cathode delivers 1.91 V at a current density of 1 A cm<sup>-2</sup> and maintains stable operation for over 150 h at 500 mA cm<sup>-2</sup>. Accelerated degradation tests exhibit minimal voltage drift, confirming the robustness of PH-FCO for industrial-scale alkaline water electrolysis.