Process for preparing linear unsubstituted .beta.-phase quinacridone pigments A process for preparing linear unsubstituted .beta.-phase quinacridone pigments or pigment preparations, which comprises a) cyclizing 2,5-dianilinoterephthalic acid in polyphosphoric acid or polyphosphoric ester with a phosphorus pentoxide content of at least 84% by weight to form the quinacridone, b) subsequently hydrolyzing this quinacridone with water or with an aqueous mineral acid solution, preferably orthophosphoric acid solution, at a temperature of at least 40.degree. C., preferably from 60.degree. to 105.degree. C., to form the crude quinacridone pigment which is predominantly in the .alpha.-phase, c) then heating the crude .alpha.-phase quinacridone pigment to a temperature between 120.degree. and 200.degree. C. in the presence of a from 0.1 to 3% strength by weight, preferably from 0.2 to 2% strength by weight, inorganic base in water and alkali-stable organic solvents, for the change of phase into coarsely crystalline crude .beta.-phase pigment, and d) subjecting the coarsely crystalline crude .beta.-phase quinacridone pigment, for the fine division to form a pigment or prepigment, to dry or wet milling; and then isolating the resulting finely divided .beta.-phase pigment; e) or subjecting the finely divided .beta.-phase prepigment obtained in d) to a finish treatment in the presence of solvents, and then isolating the pigment.