it may well be both units have bad batteries. it takes more power/current to lift to dead head than to lift and drive.
As I use it here, "phase" has to do with the AC input lines, (sometimes called the mains) and includes the input line fuses and should be an voltage equal reading between any 2 of the 3 main lines if it is a 3 phase AC, and that number should be at the number the jumpers are set at.
As far as how you read it; with one hand in your pocket and with training in how to work on AC power lines (might be a good time to call an electrician, if in the USA, for insurance reasons).