Femoral implantation of regenerated cellulose hydrogels revealed their biocompatible and osteoconductive properties, but a complete osseointegration could not be observed. Phosphorylation was therefore envisaged as the means to enhance cellulose bioactivity. Once implanted, phosphorylated cellulose could promote the formation of calcium phosphates, having therefore closer resemblance to bone functionality and assuring a satisfactory bonding at the interface between hard tissue and biomaterial. In the present work, regenerated cellulose hydrogels were surface modified via phosphorylation. Phosphorylated materials, having varying degrees of substitution, were soaked in a Simulated Body Fluid (SBF) solution in order to investigate their ability to induce the formation of a calcium phosphate layer. Mineralization was assessed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy. It was demonstrated that the calcium salt of cellulose phosphates mineralized at a higher extent than materials only phosphorylated. The degree of phosphorylation influenced the extent of surface mineralization. Moderate degrees of surface phosphorylation promoted the highest extent of mineralization. This was attributed to inadequate functionality of the surface in terms of density of PO4 groups and overall surface charge, in the case of low and high phosphate contents.