As an editor, I read about many subjects.

In this editorial, an editor of the journal Nature Chemistry explains the choice to use sulfur, not sulphur, in that publication.

In brief, the naming of chemical elements is determined by an international organization (much as an international group of astronomers decided that Pluto should no longer be classified as a “planet”), so the differences in spelling that are frequently found in the U.S. and the U.K. (e.g., color/colour) are irrelevant.

As the article notes, the chemical element phosphorus (a noun) is often confused with phosphorous, which is the adjective used to refer to something “relating to or containing phosphorus.” (To further confuse things, there is also a “phosphorous acid”!)

I frequently advise people to look up the spelling (and meaning) of words they don’t use often if they have any doubts about correctness. But in this instance, so many reputable publications use “phosphorous” instead of “phosphorus” that a quick search would not reveal the error.

Correct:

phosphorus

sulfur