How to determine which is the phase A and B of the two phase four step motors?
If you need to change the direction of the step motor you can put the output line of the drive A +. A - and; B +. B - the opposite is ok;
It's not clear your question; A four-wire step motor is represented by two winding coils in the motor, usually labeled "A +; A -; B +; B - '", which can be measured by A meter. If there is no multimeter in the field, you can also shorten two sets of two lines. If the motor is unable to rotate, the two lines representing a short connection are the same set of winding;
In fact A, B is relative. If the motor is flipped, just swap the two.
