The largest reservoir of phosphorus in the biosphere is the

Solution (By Examveda Team)

The largest reservoir of phosphorus in the biosphere is the Rocks.
Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals.
The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxide (P₂O₅). Areas of oceanic upwelling cause the formation of phosphates.