Phosphide is a compound, not an element. It's an anion, specifically the phosphorus anion (P^3-). It combines with other elements to form phosphides.

For example, you might have:

* Sodium phosphide: Na₃P

* Calcium phosphide: Ca₃P₂

* Iron phosphide: FeP

So, while phosphide itself is just the phosphorus anion, it forms compounds with other elements.