In conclusion, we have demonstrated that phosphite can be accessed via direct reduction of polyphosphates by simple metal hydrides, using mechanochemical methods. Unlike the thermal process, this direct process bypasses the hazardous intermediate white phosphorus, and ostensibly does not traverse lower phosphorus oxidation states than +3. Optimization of reaction conditions revealed that high phosphite production yields and good selectivity can be achieved when employing linear phosphates as phosphate sources with KH as the hydride source. The optimized protocol employing pyrophosphate, which contains only the poor leaving group orthophosphate, gives high selectivity for the targeted P(V)→ P(III) reduction. Mechanistic studies revealed that (poly)phosphorylated phosphite species that are generated through either ring opening of cyclic phosphates by hydride or phosphorylation of formed phosphite are key intermediates in the overreduction pathways observed when not using pyrophosphate as the P source. By using bioproduced polyphosphate from baker's yeast, we demonstrated that polyphosphates recovered from microorganisms could be promising starting materials for sustainable production of phosphite, while certain impurities may be detrimental to the efficiency of production. With this case study we lay down an idealized framework for generating an industrially useful P(III) chemical that bypasses toxic and high-energy intermediates and presents an opportunity to move toward a 'closed-loop' phosphorus industry.