Metallic Nanowire Filled Membrane (NaM) exhibit immense potential in enhancing liquid crystal phase shifters (LCPSs) performance. However, conventional numerical calculation methods are inadequate for accurately simulating LCPSs loaded with NaM due to the significant dimensional disparities between the nanoscale NaM and the millimeter or even centimeter-scale LCPS. In this paper, a novel calculation technology is proposed to accurately simulate the electromagnetic (EM) response of LCPSs integrated with NaM, including phase shift and figure of merit (FoM). The effective constitutive tensors of the NaM are extracted and utilized to construct the EM model for characterizing the NaM properties. Three NaM-LCPSs are simulated using the proposed EM model and compared with measurement results. The findings reveal that the proposed calculation method exhibits an error of less than 20%, while previously reported numerical calculation method demonstrated error as high as 60%. Furthermore, leveraging the proposed calculation method, the performance of a NaM-LCPS is optimized by systematically varying its dimensional parameters. The results demonstrate a substantial improvement in the FoM of the NaM-LCPS, increasing from 67°/dB to 120°/dB, significantly expanding the potential applications of NaM-LCPSs.