Simple answer:  No.  At least not at the moment.  I suppose over time, this can be a reality. And here’s why:  For modern cars using key-less systems to open the car, the “car key” does its job by sending radio wave signals to a receiver inside your car.

Once received and acknowledged as the right signal frequency, the door locks are released.  Since the key uses radio waves and the cellphone doesn’t, at least not in range, you can’t use it.  All wireless entry devices are mandated by law to use 300 and 500 MHz frequencies, while all cellphones are regulated to operate at 800 MHz or higher.  The cellphone just emits at the wrong frequency range.