Two-phase water-cooled heat exchangers, owing to their high heat transfer efficiency and compact structure, exhibit promising application prospects in aviation thermal management systems. With the support of the advanced interface-resolved technique, the incorporation of a reasonable phase change model becomes crucial for accurately simulating the flow boiling characteristics in two-phase water-cooled heat exchangers. However, the uncertainty of empirical factors and the complexity of phase change theories pose great challenges to the development of phase change models. This paper proposes a finite-interface-heat-flux phase change model, which converts the interfacial heat flux into phase change source terms for the cells within the finite interface by considering the interface position in the interfacial cell. First, the proposed model is validated by one-dimensional Stefan and two-dimensional pool boiling benchmark problems, yielding deviations of 3.33% and 1.2% for the instantaneous interface position and the time averaged Nusselt number, respectively. Then, the model is validated by a three-dimensional microchannel boiling benchmark problem, resulting in a deviation of 4.48% in terms of the instantaneous bubble diameter. Finally, the model is validated by a flow boiling experiment and presents the lowest deviation of 14.4% in terms of the wall superheat, while the simulation result of the flow pattern is consistent with the predicted ranges of the flow regime criteria. The proposed model outperforms the existing phase change models, showing great potential in providing a reliable numerical tool for the design and optimization of two-phase water-cooled heat exchangers in aerospace.