Phosphosus has an of ##[Ne] 2s^2 2p^3##

Phosphosus has an of ##[Ne] 2s^2 2p^3##. Therefore, it has a dot digram in the red of two electrons on top and one electron on each side. Providing for three open sites.

Hydrogen has an electron configuration of ##1s^1##. Therefore, it has only one electron on top. Each of the three hydrogens will fill one of the empty spaces of the phosphorus atom in a covalent bond. This will provide eight electrons for phosphorus, to complete the rule of octet.

Each hydrogen now has two electrons to complete the rule of duet.