The reaction involves the formation of various compounds in a stepwise manner:

Phosphorus $P$ reacts with Oxygen $O$ to form Phosphorus Pentoxide $P2O5$Phosphorus Pentoxide $P2O5$ undergoes a further reaction $representedbyX$ to convert into Sodium Phosphate $Na3PO4$Sodium Phosphate $Na3PO4$ then reacts with Calcium ions $Ca$ to form Calcium Phosphate $Ca3(PO4)2$