Poly(phthalazinone ether ketone) (PPEK), a poly(aryl ether ketone) (PAEK), has good thermal stability, nitrogen-containing functional groups, and bone-like mechanical properties. However, its surface biological inertness limits its application in biomedical applications. This paper presents the synthesis of PPEK modified with quantitative introduction of phosphonate groups (PPPEK) by a simple wet chemical modification method. The biomineralization process is regulated by the number of phosphonate groups, and a coating similar to bone apatite is deposited on the surface of PPEK substrates, thus greatly improving the biocompatibility of the material surface. The chemical structures of PPPEK are confirmed by 1 H NMR and FTIR. Microstructural and compositional studies performed by SEM, TEM, XPS, and XRD reveal that apatite coating is significantly enhanced with the increase in the phosphonate groups on the PPEK substrate. In addition, cell culture studies show that apatite coating induced by PPPEK promoted cell viability, cell adhesion, and osteogenesis of MC3T3-E1 cells.