I can see what the problem is....if you look at Cs on the Periodic table its a +1 (i forgot what their called valance electrons maybe?) and Cl is a -1. So when you do the criss-cross rule, they cancel out since its 1 to 1. So it should read CsCl. You do that for all the elements. For PO4, I believe you have to look in your chem book because its a polyatomic ion. According to table 9.3 in my book, PO4 reads at a charge of 3-. So for your Ca and PO4 Ca is a 2+ charge and PO4 is a 3-. When you do the criss-cross rule, it becomes Ca3(PO4)2. Then after all that you should be able to start balancing....hope this helps!!