Firstly you have forgotten to divide by 4 because the standard phosphorus allotrope the white phosphorus consists of molecules P4. After that you should divide the obtained value by Avogadro's number. How have you obtained such a large value? It is seemed that you added 23 to 25 in power, while it should be subtracted.
i did not get that. i divided 1.20 x 10^25 by Avogadro's number and i got 1.99 x 10^47 mol P
Each molecule of P<sub>4</sub> contains 4 atoms, that's why there's that "4" factor
Were is the 4 coming from