If you tell us what you are actually asking, it might help.
Do you mean using a smart phone to negotiate a call to an analogue modem using it's speaker? YES (technically, I've never seen it done).
Or connecting your phone to the serial port of a PC and to a the phone line? NO, although you might find an old GSM handset which can do this.
Or using your phone to tone dial for you? YES (again, I've not seen it done).