Good software comes with EDS spectrometer, so you already have it. In addition you need a good standard (certified hydroxyapatite will do) and a good EDS operator. Set your software to analyze Ca and P and as a "ballast" element you can set O or some combination of O and C if your software allow it. If you want to analyse not only Ca and P, but light elements also, you'll need more standards and really excellent operator.