Dynamic covalent networks are a class of polymeric materials that combine the merits of classical thermosets and thermoplastics, in terms of mechanical properties and reprocessability, in one material. Various dynamic covalent chemistries have thus been implemented in polymeric materials with recent interests shifting toward chemistries that would allow rearrangements in network topology without the aid of external catalysts. Here we introduce transesterification in phosphate triesters as a new dynamic covalent chemistry in polymeric networks. A simple one-step synthetic strategy has been utilized to synthesize polytetrahydrofuran networks with phosphate triester cross-links. The materials showed finite viscous flow at elevated temperatures via transesterification at the cross-links without externally added catalyst. This approach provides an easy method for cross-linking OH-end-functionalized polyethers and has the potential for general use with other OH-functionalized polymers.