Put the seat belt around your phone in the passenger side?
This...take a look up near the front interior lights in the middle, you'll see the "put your seatbelt on" symbol flashing up there. You probably have something on the passenger seat that is tricking the car into thinking you have a passenger without the seatbelt fastened. Or in fact you have a passenger without the seatbelt fastened. Or you have a passenger sometimes out of the blue who has five bongs and doesn't care to wear his seatbelt.
Steverino's comment is about you (and others) posting about a problem but not specifying which model year you have, build dates are helpful too (and easy to find), trim level is bonus. Information that is helpful in having the forum help you. Think Jerry Maguire.