The date palm tree is extensively cultivated in Middle Eastern countries such as Saudi Arabia, generating a large amount of waste in the form of leaves, seeds, and fibrous materials. This study examined the feasibility of using raw date palm fiber (RDPF) and NaOH chemically modified date palm fiber (NaOH–CMDPF) obtained from discarded agricultural waste for the removal of phenol in an aqueous environment. The adsorbent characterization was performed by using different techniques, i.e., particle size analysis; elemental analyzer (CHN); and BET, FTIR, and FESEM-EDX analysis. The FTIR analysis revealed the presence of various functional groups on the surface of the RDPF and NaOH–CMDPF. The results showed that chemical modification by NaOH increased the phenol adsorption capacity that was well-fitted by the Langmuir isotherm. Higher removal was obtained with NaOH–CMDPF (86%) than with the RDPF (81%). The RDPF and NaOH–CMDPF sorbents’ maximum (Qm) adsorption capacities were more than 45.62 mg/g and 89.67 mg/g and were comparable to the sorption capacities of various other types of agricultural waste biomass reported in the literature. The kinetic studies confirmed that the adsorption of phenol followed the pseudo-second-order kinetic process. The present study concluded that the RDPF and NaOH–CMDPF were eco-friendly and cost-effective in promoting sustainable management and the reuse of the Kingdom’s lignocellulosic fiber waste material.