You should set up a VoltageRatioChange event handler, this function will trigger whenever the voltage changes. Then you just need your program to look at the value and decide how you want the object to move.
You should take a look at this sample project:
Dial Phidget with Unity
This project uses the encoder and digitalInput object instead of VoltageRatioInput, but it should give you an idea of what your program will need to look like in order to control a character with Phidget input that comes from events.