Phosphorous in chemical compounds has many uses, good and bad. It is important in plant and animal growth, in bone formation in the body, etc., etc. The element phosphorous is never found pure in nature and is extremely dangerous- see post by Peace, above.

The same may be said of the element sodium, also extremely unstable and dangerous and never found pure in nature, but when combined with elemental chlorine, a deadly gas, forms our table salt and makes the seas salty.