A phosphoramidate is a phosphate that has an NR2 instead of an OH group. The structure of phosphoramidic acid (phosphoramidate), (HO)2PONH2, is present in PubChem.
A phosphorodiamidate is a phosphate that has two of its OH groups substituted by NR2 groups.
Two examples of natural phosphoramidates are phosphocreatine and the phosphoramidate formed when histidine residues in histidine kinases are phosphorylated. An example of a phosphorodiamidate is Morpholino which is used in molecular biology.