Both white phosphorus and red phosphorus are made up only of phosphorus atoms. does this mean they are both pure substances? could they be compounds?

True, both of the red and white phosphorus is a pure substance.

Both red and white phosphorus is made of phosphor element but they have a different structure which causes them to have a different color. This phenomenon called allotropes when a chemical element has two or more different form.They are not compounds as they are only made of phosphorus. A compound should be made by at least two different elements.

Chewy,wrapped,not in all white,the wrapper is clear