IRNA PHILLIPS, NBC author holds the radio record for the length of time she’s been writing daily script serials without intermission, is a stickler for realism when it comes to the business of writing her own shows.For instance, not a single line of her new program, “The Woman In White,” five-a-week serial dealing with the lives, ambitions and sacrifices of trained nurses in America, was set down on paper until Irna had personally interviewed dozens of Twentieth Century Florence Nightingales, had made tours of inspection of every available Chicago hospital and had completed extensive research on the history of nurses in this country.