Phosphorus is the second element of group (v) with atomic number 15 and the electrons per shell are arrange as thus; 2, 8, 5.
The electronic configuration of phosphorus is
₁₅P = 1s² 2s² 2p⁶ 3s² 3p³
Or
₁₅P [Ne] 3s² 3p³
In its first shell I.e 1s shell, it has 2 electrons filling it to s-orbital requirement. In its second shell, electrons fill it in 2s² 2p⁶ filling the second orbital and attaining an octet configuration. The third shell contains 5 electrons filling 3s² 3p³ orbital.