An organic hydroxyl compound is reacted with a phosphorylating agent comprising phosphorus pentaoxide and at least one compound selected from the group consisting of water, phosphoric acid and polyphosphoric acid and having a value represented by formula (I) of from 0.5 to 1.0, under such a condition that the ratio as defined by formula (II) has a value in the range of from 2.8 to 3.2; or alternatively, an organic hydroxyl compound is reacted with the above phosphorylating agent under such a condition that the ratio as defined by formula (II) has a value in the range of from exceeding 3.2 up to 6.4 and then phosphorus pentaoxide is added to the reaction product in such an amount that the ratio as defined by formula (II) has a value in the range of from 2.8 to 3.2 with respect to the total feeds of the starting materials to conduct further reaction: ##EQU1## The above process produces a phosphoric ester mixture that is excellent in hue and odor, is reduced in the amount of orthophosphoric acid and contains a phosphoric monoester useful as a component of a detergent.