It needs 5 electrons. I would start by looking at a periodic table. The numbers on top are group numbers. Below each number is roman symbols like (lA, llA, IIIB, etc.). Phosphorus is in group 15. Under fifteen it has the Roman numeral of 5 (VA). There is a pattern in the periodic table. Each Roman numeral stands for how many valence electrons it has. Valence electrons are the outermost electrons of an atom.
