From Longman Dictionary of Contemporary Englishbe on the telephonebe on the telephonea) TCTTELEPHONEto be talking to someone, using the telephone I was on the telephone when he came in. b) TCTto have a telephone in your home, office etc → telephone
Examples from the Corpus
be on the telephone• From 6am Brown is on the telephone.• The Sheikh arrived while the doctor was on the telephone to the hospital.• I told him who I was on the telephone.• She loves to be on the telephone.• She must not ask who was on the telephone. 