Hello!
The formula for Copper (II) Phosphate is
Cu₃(PO₄)₂
To know how to write this formula we go from left to right. First, Copper (II). It means that the formula has the Cu⁺² ion. Now, Phosphate means that the compound has the PO₄⁻³ ion. Now we combine this two ions, giving to each one the coefficient with the number of the electric charge of the other (e.g. to Cu⁺² we'll give the charge of PO₄⁻³ which is 3 and the result will be Cu₃⁺²).
The combination gives us the result Cu₃(PO₄)₂
Have a nice day!