In this work, we report on enhanced adsorption of anionic dyes, Reactive blue 49 (RB 49) and Direct Blue 199 (DB 199), using a phytic acid-doped poly-N-phenylglycine@potato peel (PA-PPG@PP) nanocomposite material. The PA-PPG@PP was prepared using a radical polymerization process by varying the amount of potato peel powder (PP) in the composite material. The surface structure and composition were examined by zeta potential, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) analysis. The influence of different operating conditions such as adsorbent dose, initial dye concentration, contact time, pH and ionic strength on the removal efficiency of PA-PPG@PP2 was assessed to achieve the optimum conditions for RB 49 dye adsorption. Adsorption equilibrium data were well-described by the Langmuir model and the maximum adsorption capacities of PA-PPG@PP2 for RB 49 and DB 199 at 298 K and pH = 6.5 were 216 and 1148 mg g−1, respectively. The maximum adsorption capacity of RB 49 dye on the PA-PPG@PP2 surface was achieved at 318 K (285 mg g−1). The adsorption process was described by the pseudo-second-order kinetics model (R2 > 0.999). The thermodynamic study proved that the adsorption processes were endothermic and favorable. The dye molecules were adsorbed on the composite material surface mainly through hydrophobic and electrostatic interactions, as well as hydrogen bonding. Additionally, our experimental results suggested that the hydrophobic interactions increased upon increasing ionic strength, while the electrostatic interactions decreased upon elevating the ionic strength of the solution. The findings in this work revealed the potential of biomass powder, potato peels, in adsorption processes upon hybridization with a biocompatible organic polymer, poly-N-phenylglycine.