Effect of temperature on processes occurring in carbothermic reduction of phosphorus from mixtures and melts based on calcium phosphate with silica was studied. The process was thermodynamically simulated using the software package Astra. Data on parameters of the equilibrium state of the system in the temperature range 1400–2300 K were obtained. At temperatures higher than 1773 K, the reduction of phosphorus is accompanied by a silicon-reduction process. Above 2000 K, the yield of SiO becomes comparable with that of phosphorus. The optimal temperature range for performing the process used to obtain phosphorus is 1623–1773 K. For this condition to be satisfied, it is necessary to preclude appearance of an electric arc in furnace aggregates.