The phosphine-Ar (PH3-Ar) van der Waals complex's three-dimensional potential energy surface (3D-PES) was mapped along the intermonomer coordinates using the explicitly correlated Coupled Clusters approach. An analytical expansion of this 3D-PES is deduced. The complex characteristics of the intermolecular interactions between PH3 and Ar, which are at the origin of the pressure broadening of the PH3 rovibrational lines, are accurately described by this 3D-PES. Afterwards, the broadening of the phosphine lines perturbed by Ar at room temperature is computed using this 3D-PES. To be able to incorporate this 3D-PES into our collisional broadening computation software, we first modified it with a new "fractional" function. Then, we used the semiclassical Modified Robert and Bonamy model improved by the so-called notion of exact trajectory. For various branches of the ν2 and ν4 PH3 rovibrational bands, room temperature data are provided. Our data agree with the experimental measurements. The precise estimation of PH3 and Ar abundances in planetary atmosphere spectra should benefit greatly from the data provided here.