Upgrading of calcareous phosphate ores by reverse flotation in acidic media depends mainly on the chemical reagents used, especially the collectors. Anionic collectors are commonly used in phosphate flotation circuits; however, in the most cases each collector was tested separately. Although using the mixture of the anionic collectors in salt-type minerals flotation is very limited, it has several advantages over using each collector alone. Therefore, in the present paper, the mixture of oleic acid and sodium dodecyl sulfate (SDS) was tested and compared to the usage of each collector individually. A number of experiments were conducted to find out the optimal reverse flotation conditions for each collector in terms of collector dose, pH, and oleic acid to SDS (Ol:SDS) mixing ratio as main variables using factorial design. The design results showed that the Ol:SDS mixture, particularly at 1:1 mixing ratio, improves the phosphate grade with slight decrease in recovery in comparison with using each collector separately. The highest concentrate grade (>33% P2O5), with a recovery of 85%, was obtained at pH 6, 1:1 Ol:SDS mixing ratio, and collector dose 3.5 kg/t. In addition, using 1:1 mixing ratio drastically lowers the collector dose from 3.5 to 2 kg/t or even lower depending on the pH to achieve the concentrate grade required by phosphate industry (30% P2O5). [ABSTRACT FROM PUBLISHER]