Analog input voltage rises when motor is working
Try adding some bypass capacitors at the two points I've added arrows to:

I suggest two in each spot, one a 0.1uF (or similar) ceramic dipped or disc and the other a 1 or 10uF electrolytic.  Keep the polarity in mind for the electrolytic.
Oh, and another thing.  Be sure your motor is not pulling your power supply voltage down.  It's possible your phone charger supply is inadequate to supply the power needs of the motor.  Use a voltmeter across the input to the Arduino and check the voltage when the motor runs.  If it's dropping much below 5V you need a better power supply.  Well, I see now that you are only powering the motor from that 5V supply.  So that's probably not it.