A method of synthesis of phenylhalosilazanes by the reaction of phenyl(fluoro)chlorosilanes PhSiF3-n Cl (n) (n = 0-3) with hexamethyldisilazane at room temperature is elaborated. The thermolysis of 1,1,1-trimethyl-3-phenyl-3,3-difluorodisilazane affords cyclic phenylfluorosilazanes (PhSiFNHSiMe3)n (n = 3-5). The process may occur via the intermediate formation of phenylfluorosilimine.