Indium phosphide (InP) semiconductors play an irreplaceable role in optical communication, and with the expansion of the market scale, the amount of InP scrap, which has become an important secondary resource for recovering phosphorus and indium, has considerably increased. However, as a typical phosphorus containing material, InP scrap recycling is difficult and dangerous because phosphorus is flammable and releasing toxic and irritating smoke during combustion. In this study, a safe, clean, and sustainable “controlled-pressure pyrolysis–spray condensation” process is proposed. Firstly, InP is decomposed into phosphorus and indium under high-temperature conditions; phosphorus then evaporates into the vapor phase and is sprayed with warm water for condensation in water, whereas indium is enriched in the liquid phase. The feasibility of this process is proven by performing thermodynamic calculations and scaled-up experiments (hundred grams to kilograms) by using a self-designed equipment. At a decomposition temperature of 1323 K, micro-negative pressure, and holding time of 5 h, an indium ingot with a purity of 99.59 wt.% was obtained and the direct yield reached 98.2%. Industrial α-yellow phosphorus with a purity of >98 wt.% was obtained and safely stored in water, and the comprehensive recovery rate is >90%. The overall process produces zero waste gas, liquid, or residue. The new process is easy to implement in industrial applications when the equipment is fitted with a continuous feeding and discharging system. A convenient and safe method for the X-ray diffraction detection of yellow phosphorus is also developed in this study.