The present study concerns the investigation of a material expected to be biocompatible and able to promote bone regeneration. For this purpose, cellulose was chemically modified by phosphorylation. Once implanted, phosphorylated cellulose could promote the formation of calcium phosphates, thus having closer resemblance to bone functionality. In a previous investigation, the obtention and the preliminary characterization of cellulose phosphate gels were reported. In the present study, the synthesis by the H3PO4/P2O5/Et3PO4/hexanol method was optimized in terms of reaction parameters. The structure of materials was investigated by FTIR, Raman, and solid-state P-31- and C-13-NMR spectroscopic studies, and X-ray diffraction. Water swelling and stability to sterilization by gamma-radiation were also assessed. It was demonstrated that the present method allows highly phosphorylated cellulose derivatives to be obtained. Cellulose triphosphates gels are described here for the first time. Products obtained were poorly crystallized monoesters, apparently not significantly affected by gamma sterilization and showed a high water swelling capability. Chemical bonding was confirmed by FTIR, Raman, and both P-31- and C-13-NMR spectroscopies. It was also shown that the H3PO4/P2O5/Et3PO4/hexanol method provides a versatile and interesting alternative route to some of the more widely used techniques for the phosphorylation of cellulose.