<p>This study introduces a novel and environmentally relevant sample preparation strategy for the trace-level determination of hazardous phenolic pollutants in complex wastewater matrices. Unlike conventional extraction methods that merely tolerate matrix interferences, this approach eliminates them before analyte extraction, improving selectivity and reliability. A magnetic core–shell metal–organic framework was employed to selectively adsorb interfering substances from real wastewater samples collected from pharmaceutical, municipal, and petrochemical sources. This material was characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and Brunauer–Emmett–Teller surface analysis. Its magnetic responsiveness allowed for simple and rapid phase separation without the need for centrifugation. Following matrix cleanup, phenolic compounds were derivatized using acetic anhydride in the presence of sodium carbonate and extracted using a vortex-assisted liquid–liquid microextraction technique. The optimized method required minimal amounts of sorbent and organic solvents, improving its environmental sustainability and reducing laboratory waste. Coupled with gas chromatography and flame ionization detection, the method demonstrated excellent analytical performance, with relative standard deviations between 1.0 and 8.3% (for 10 µg L⁻¹), recoveries ranging from 62 to 83%, correlation coefficients above 0.9962, and low limits of detection and quantification. Application to real wastewater samples showed recoveries between 81 and 118%, confirming the method’s effectiveness in eliminating matrix interferences and accurately determining phenolic pollutants.</p>