I assume you are referring to tricalcium phosphate. The molar mass of this compound is 310.18 g/mole. 660 grams of tricalcium phosphate has 660/310.18 = 2.127 moles of tricalcium phosphate.

We need to make 2.5 L of solution of calcium phosphate. In each liter we will have 2.127/2.5 = 0.8511 mole of tricalcium phosphate.

As the number of moles of the solute in every liter of the solution is 0.8511, the molar concentration or molarity of the solution that is produced is 0.8511.

It is possible to make 2.5 L of a solution with a molarity of 0.8511 with 660 g of calcium phosphate.