Composition containing an aqueous phase and an emulsifying system, where the emulsifying system contains at least one C10-C30 alkyl phosphate and at least one C8-C24 fatty alkyl ether of polyethylene glycol, the ether comprising from 1 to 19 ethylene glycol units and having an HLB<8 at 25° C. Process for making up or for non-therapeutically caring for keratin fibres, via the application to keratin fibres of the composition. Uses of the composition in particular for obtaining uniform and/or thick makeup on keratin fibres, and as mascara for making up keratin fibres.