Exploration of THz frequencies has enabled new applications in the areas, where high-resolution short-range remote sensing is of great interest. At the high frequency ranges like THz or sub-THz, synthetic aperture radar (SAR) image formation algorithms are highly sensitive to platform deviations, which motivates the development of new algorithms that are capable to handle this problem.In this paper, we introduce a modified linear interpolation algorithm with the phase-control procedure for the three-dimensional (3D) global backprojection (GBP) algorithm. The procedure assigns the actual time needed for the signal to be transmitted to the given point in the defined image plane and collected by the receiver into the phase of the complex SAR data. The algorithm has been verified with the real monostatic and bistatic SAR data acquired in the 0.325-0.5 THz frequency band.