A) Between 5 and 15 kHz
Some people find the term, "FM phone" a little confusing when first encountered. In amateur radio, you are using FM phone when you are speaking into a microphone while transmitting using the FM mode.
The bandwidth of an FM signal varies with the signal's modulation.
The American engineering genius Edwin Armstrong invented frequency modulation (FM) radio. Armstrong presented his paper, "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation", to the New York section of the Institute of Radio Engineers on November 6, 1935.