Anisotropic materials with very high aspect ratios, such as nanoplatelets, are an exciting class of materials due to their unique properties based on their unilamellar geometry. Controlling their size and surface-functionality is challenging and has only be achieved in some cases for synthetic polymers. We present a general approach to prepare polymer-nanoplatelets with control over the lateral size and basal functionality, by simple polycondensation of precisely spaced and functional phosphate groups in polyethylene-like polymers. Because of the relatively large size of the phosphate groups, they are expelled from the bulk crystal to the basal surface. This allows to control the chain-folding during crystallization, which we analyzed via solid-state NMR and TEM. Furthermore, we present chemistry “on the surface” of the platelets: the pendant ester group at the phosphate offers the possibility to introduce functional groups accessible for further chemical modification on the crystal surface. This is shown by introducing a 2-acetylthioethyl ester group and subsequently cleaving this 2-acetylthioethyl ester group to the free P–OH. Together, these results render polyethylene-like polyphosphoesters a versatile platform for soft-matter nanoplatelets as functional colloids.