Phosphate ester bonds are widely present in nature (e.g. DNA/RNA) and can be extremely stable against hydrolysis without the help of catalysts. Previously, we showed how the combination of phosphoryl and calixarene moieties in the same organic framework (LPO) allows isolation of single lanthanide (Ln) metal ions as [LnIII(LPO)2](O3SCF3)3. Here we report how by controlling the reaction conditions a new hydrolyzed phosphoryl-calixarene ligand (H3LHPO) is formed as a result of LnIII-mediated P–OEt bond cleavage in three out of the eight possible sites in LPO. The chelating nature of H3LHPO traps the LnIII species in the form of [LnIII(LHPO)((EtO)2P(O)OH)]2 dimers (Ln = La, Dy, Tb, Gd), where the Dy derivative shows slow magnetization relaxation. The strategy presented herein could be extended to access a broader library of hydrolyzed platforms (H x LHPO; x = 1–8) that may represent mimics of nuclease enzymes.