Phillips, who started her career as a radio journalist, will broadcast every Sunday from 2pm to 5pm starting on Easter Sunday.
Each week Phillips will be talking to celebrity and topical guests as well as playing London's widest variety of music from the Sixties to the present day.
Smooth Radio programme controller Gavin McCoy says, "It's a delight to be able to welcome Fiona to Smooth Radio. She has a very warm personality and a great sense of humour and I have no doubt will entertain our listeners as much on a Sunday afternoon as she does the nation each morning".
Phillips started at GMTV 10 years ago after joining as its Los Angeles entertainment correspondent. Before that, she was a news correspondent both in independent radio and television.