"phone" displayed on radio of ford expedition 1999?

i have a ford expedition that i have owned 8 yesrs with little or no problems other than normal maint. i went to drive it today and the radio would not work it has "phone" displayed on the radio. i have never seen it do that before. does anyone know how to put this back into normal operation? i have teenage kids and have a feeling i might have had some help. none of them know anything about it....immagine that! thank you in advance for any help you can provide.