We present a phase-field model of thermally-induced phase separation in polymer solutions, calibrated for the polyvinylidene fluoride (PVDF)/diphenyl carbonate (DPC) system. Large-scale three-dimensional computer simulations were performed for isotropic and anisotropic thermal quenches, and the evolution and structure of the resulting two-phase morphology is analyzed. Isotropic quenches, in which the temperature is uniformly reduced below the binodal temperature, were conducted to understand the initiation and coarsening of the polymer-rich and polymer-poor phases throughout time. Anisotropic quenches, in which the system is cooled from one particular surface, were also conducted to understand how gradients in the characteristic domain size develop for varying conditions. In these anisotropic quenches, we observe the formation of a dense skin layer adjacent to the cooling surface, the thickness of which depends on several parameters including the polymer volume fraction, the assumed bath temperature that is maintained at the cooling surface, and the rate of thermal conduction through the polymer solution. The model here can be adapted to other polymer/solvent systems by modifying the thermodynamic and kinetic parameters specific to the two species.