Interferometric synthetic aperture radar (InSAR) has been a valuable tool for mapping topography and subtle deformations. However, dealing with a wide imaging integral angle (IIA), especially for low-frequency band unmanned aerial vehicle (UAV) InSAR systems, introduces challenges. The conventional interferometric phase model depends on the difference in two slant ranges between the synthetic aperture centers and the target in two observations. Accuracy limitations emerge when variations are encountered in differences of slant range history across the entire wide IIA. This article explores the impact of IIA on interferometric measurements and proposes a modified interferometric phase model to address these limitations. For a wide IIA, the proposed model focuses on the integral of differences in slant range history throughout IIA by considering the nonlinear trajectory of the UAV platform. Additionally, measurement models for the IIA are deduced, in which an additional scale factor expanded by the Bessel function is introduced. Simulated and experimental datasets are utilized to demonstrate improvements in the accuracy of topography and deformation measurements. These results validate the effectiveness of the modified model in overcoming the challenges posed by wide IIAs in UAV InSAR systems.