Phosphorus does not occur free in nature; it is far too reactive. It is found as phosphate, bound to oxygen, in the mineral apatite and in every living cell.
Its biological role is structural and central. The backbone of DNA and RNA is a chain of alternating sugar and phosphate. Adenosine triphosphate, the molecule that carries usable energy in every organism on Earth, works by making and breaking phosphate bonds. Bone and tooth enamel are calcium phosphate. Cell membranes are built from phospholipids. There is no part of life that runs without it.
That gives phosphate rock a peculiar economic position. Nitrogen fertiliser can be made from the air; potassium is abundant. Phosphorus can only be mined, the workable reserves are concentrated in a small number of countries, and there is no chemical substitute whatever, because nothing else does what phosphorus does inside a cell. Recovering phosphate from waste streams is an active field of engineering for exactly that reason.
The element has several forms. White phosphorus is the one Brand made: waxy, glowing, spontaneously flammable and severely poisonous. Workers in the nineteenth-century match industry, exposed to its fumes, developed phossy jaw, a destruction of the jawbone that contributed to the London matchgirls' strike of 1888 and led eventually to an international prohibition on white phosphorus matches in 1906. Red phosphorus, made by heating the white form, is stable and non-toxic, and is what appears on the striking strip of a modern safety match. Black phosphorus, the densest form, is a semiconductor and has attracted attention as a two-dimensional material.