"Polyester stabilized with a flame retardant amount of condensation product of phosphonitrilic dihalide and a brominated phenol having the formula ##STR10## wherein R is an alkyl radical of up to about 3 carbon atoms, a is an integer of value 0-3 such that the total number of carbon atoms in radicals appended to the ring is not more than about 4 and y is an integer of value 1-5; said polyester bein" . . . .