Phosphate rock, a finite and non-renewable resource on earth, is facing the dilemma of resource depletion and quality decline, thus it is urgent to fully utilize any potential phosphorus resources. In this paper, a novel process combined alkaline leaching and crystallization for phosphorus recovery from the leaching residue of montebrasite (LRM) was proposed. The main component of LRM was determined to be AlPO4. Thermodynamic study of the Al3+-PO43--H2O system was carried out, which revealed that the complete dissolution region of AlPO4 were pH < 0.8 and pH > 12.2. Using NaOH as the leaching agent, a series of single factor experiments were conducted to determine the optimal leaching parameters. The results demonstrated that the extraction rates of P, Al and Si were 89.40%, 86.49% and 23.33%, respectively, at leaching temperature of 60 °C, leaching time of 1 h, liquid-to-solid ratio of 12 mL/g and NaOH concentration of 120 g/L. Moreover, phosphate in leach liquor was recovered in the form of Na3PO4 by crystallization. The recovery rate of P in leach liquor reached 95.72% at 5 °C for standing 24 h, whereas only 6.51% of Al was lost. The process proposed in this study provides the possibility of extracting phosphorus from a new potential phosphorus resource.