First off a transistor is not a variable anything it's an on/off gate. What do you want to control an incandescent light bulb? Something else? Generally speaking if your not sure what a transistor does stay away from mains voltages it can kill you. That said a 6 buck ebay Bluetooth module attached to a 6 buck solid state relay and you can control it from a smartphone with your own app via pwm dimming. There are also at least a half dozen ways to do something like this. Honestly though a few buck x10 module can do this.