The orbital diagram for phosphorus consists of five electrons in the third shell, eight in the second and two in the first shell, closest to the nucleus. The atomic number of phosphorus is 15. This number indicates the total number of electrons.
An atom is made up of the nucleus, which is surrounded by shells. The atom's electrons orbit around the nucleus on these shells. In any atom, the first shell can only hold up to two electrons, and the second and third shell can each only hold up to eight electrons. That holds true for the first 18 elements in the periodic table.
It is very easy to draw an electron configuration of any element. The only type of information that is required is the atomic number. Because the atomic number is equivalent to the number of electrons, the standard electron configuration can be used to draw the orbital diagram. With an atomic number of 15, two electrons go in the first orbit and eight go in the second. Because 8 + 2 = 10, there are five remaining electrons. These have to go into the third because the first and second orbits are full. The placement of the electrons on each orbital ring does not matter. However, it is helpful to number the electrons on each ring.