Question: how many moles are 1.20 x 10^25 atoms of phosphorus?
Answer: For phosphorous or any chemical compound, a mole contains 6.022⋅1023 molecules in it. So if you have 1.20⋅1025 (that's what I assume you meant) atoms of phosphorous, then just divide by Avogadro's number to find the number of moles.