Cellulose regenerated by the viscose process was previously investigated as an implantable material in orthopedic surgery. It was envisaged to take advantage not only of its good matching with mechanical properties of bone but also of its hydroexpansivity, therefore allowing a satisfactory fixation to hard tissue. Both the osteoconduction and the lack of osteoinduction of this material were demonstrated. Grafting of phosphate groups was then envisaged as the means to render cellulose more suitable for orthopedic applications by enhancing its bioactivity. In the present work, the previously optimized phosphorylation reaction was successfully adapted to the surface modification of regenerated cellulose. Modified materials were characterized by XPS, FTIR, and P-31 MAS NMR spectroscopic studies, and contact angle measurements, revealing the chemical bond between phosphate groups and cellulose, as well as the hydrophilic nature of phosphorylated materials, which increases with increasing phosphate contents. Water swelling and resistance to gamma sterilization were assessed as well, showing that phosphorylated materials swell considerably in water and were not affected when sterilization was carried out under a nitrogen atmosphere. The increase in surface roughness attributed to chemical modification was demonstrated through laser rugosimetry measurements.