To effectively address the challenges of poor selectivity and limited applicability only under weakly alkaline environment of traditional cationic collectors for reverse flotation of silica removal from phosphate, a novel high-efficiency cationic collector SDTQ has been developed that is suitable for weakly acidic environments. Flotation tests were conducted using this reagent on a siliceous-magnesium phosphate from Guizhou Province. The results show that under the conditions of pH 6 and SDTQ dosage of 25 mg/L, the pure quartz sample showed a flotation recovery of approximately 100% while pure fluorapatite sample showed negligible floatability. With the sample of artificial mixture of quartz and fluorapatite, effective separation of fluorapatite from quartz was achieved under the flotation conditions of pH 6 and SDTQ dosage of 100 mg/L. Parametric flotation tests conducted with the actual phosphate sample, which was the concentrate from the magnesium removal flotation at pH 6, determined the optimum SDTQ dosage to be 1.1 kg/t. Under this reagent dosage, open-circuit flotation tests generated the separation performance of 35.38% P2O5 grade, 85.40% P2O5 recovery, and 5.53% acid insoluble (A.I.) content in the phosphate concentrate. Finally, a good performance of 35.49% P2O5 grade, 90.31% P2O5 recovery and 9.81% acid insoluble (A.I.) content in the concentrate was obtained from the closed-circuit flotation flowsheet of one rougher, one cleaner, and one scavenger. Compared with dodecylamine, SDTQ increased the grade of phosphate concentrate by 2.05 percentage points and the recovery by 10.02 percentage points. Zeta potential and contact angle measurements revealed that the key mechanism lies in SDTQ's selective adsorption on quartz surfaces through electrostatic interactions, which enhances the difference in hydrophobicity between quartz and fluorapatite, thereby enabling efficient silicon removal in reverse flotation of phosphate. The results of atomic force microscopy and infrared spectroscopy showed that the SDTQ collector acted on the surface of quartz in the form of physical adsorption by means of the synergistic effect of quaternary ammonium cationic groups and long-chain alkyl groups. SDTQ collector improved phosphate concentrate grade and reduced reagent costs, delivering dual economic and environmental benefits.