Determine the number of valence electrons for each atom.

Step 1: Determine the number of valence electrons for each atom.
Phosphorus (P) is in Group 15, so it has 5 valence electrons.
Hydrogen (H) is in Group 1, so it has 1 valence electron.

Step 2: Calculate the total number of valence electrons for the phosphonium ion ($\text{PH}_4^+$).
The positive charge indicates that one electron has been lost.

$$\text{Total valence electrons} = (\text{Valence electrons of P}) + (4 \times \text{Valence electrons of H}) - (\text{Charge})$$ $$$$