Phosphazene-containing oligomers (FEO) were synthesized by the one-pot method by reacting hexachlorocyclotriphosphazene, diphenylolpropane, and epichlorohydrin at 80 °C in the presence of solid KOH. In contrast to analogous oligomers previously obtained at a lower temperature, according to MALDI-TOF spectrometry data, they contain about 10% of compounds with two or three phosphazene rings linked by one or two oxyaryleneoxy radicals, while the total number of epoxy groups in the molecules of these compounds is from 4 to 8. FEO are cured with polyamine hardeners to form compositions with increased fire resistance, retaining at the same time the basic properties of conventional epoxy materials.