The interaction between corrosion and fatigue represents a highly complex, strongly coupled chemo-mechanical degradation process that critically affects the durability of reinforced concrete structures exposed to chloride-rich environments and cyclic loading. Corrosion of steel reinforcement induces cracking and loss of cross-section, increasing stress concentrations and accelerating fatigue damage, while fatigue-driven cracking in concrete enhances chloride ingress and promotes further corrosion. These mutually reinforcing mechanisms lead to nonlinear degradation and significant reductions in service life, which cannot be captured by conventional sequential corrosion-fatigue analyses. This contribution presents a fully coupled multiphysics phase-field modeling framework for corrosion-fatigue interaction in reinforced concrete. The framework consistently resolves the co-evolution of key physical processes, including chloride transport in concrete, corrosion initiation and reactive transport of iron species, rust precipitation and pressure buildup at the steel-concrete interface, corrosion-induced degradation of steel, fatigue damage in reinforcement, fracture and fatigue crack propagation in concrete, and damage-dependent transport properties. By embedding these processes within a unified chemo-mechanical formulation, the model explicitly captures feedback mechanisms between chemical degradation and mechanical damage. The framework is implemented in FEniCS [https://doi.org/10.25835/3duuzvj4] and demonstrated through two-dimensional representative rebar configurations and a three-dimensional reinforced concrete beam. Numerical results reveal how corrosion state, loading history, and cyclic loading sequence govern crack initiation, corrosion kinetics, and fatigue lifetime. The simulations show that conventional corrosion-followed-by-fatigue approaches systematically underestimate structural performance, while the fully coupled model provides physics-based predictions of degradation and lifetime. The proposed framework offers new insights into the spatio-temporal interaction between transport, cracking, and corrosion and represents a robust foundation for advanced lifetime assessment and future digital twin applications.