Lanthanide Complexes of 2,2′,2″‐(10‐{[Hydroxy(Phenyl)Phosphoryl]Methyl}‐1,4,7,10‐Tetraazacyclododecan‐1,4,7‐Triyl)Triacetic Acid: Structural Characterisation of Intermediates from the Proposed Complexation Mechanism in the Systems of Lniii‐Dota‐Type Ligands