I believe that is generally the maximum current per phase. It's never the "required" current because you can always /under/ drive a motor. If there is a voltage rating, then you can measure the coil resistance and use ohms law to calculate the current, but that doesn't really solve the "per phase" vs "total" question.
When it comes right down to it, the amount of power you can jam into a motor is limited by two things: Heat and insulation breakdown in the windings. The insulation is only affected by max voltage... well... until it melts! The heat is affected by MANY things: Mostly by motor current times voltage which is the power the motor is accepting, but also by how much cooling you can apply, how many eddy currents are caused in the motor windings by AC components in the drive signals (choppers cause more eddy current heating) and so on. There is a limit to the torque produced by a given drive current and past the rated current you won't get more torque because the magnetic field can't help turn it anymore, but that doesn't make the motor blow up or anything.
So don't exceed the max voltage rating or the windings might short and don't let the motor get too hot, but other than that, driving more than rated current really isn't that big a deal. I've driving 2 amps through a 1 amp rated motor without any problems... and I get a /little/ more torque... maybe half again as much... as I did when driving 1 amp at the same voltage. My power supply only put out a fraction of the motors rated max voltage so I wasn't in any danger of damaging it.
Other will correct me if I'm wrong or have their own opinions, but the point is: Don't get terribly hung up on knowing the motors exact rated current. If you motor is 1.5 total and you drive it at 1.5 per phase (3 total) and just keep a finger on it to make sure it isn't overheating, you should be just fine.
There is also a lot more info on how to estimate what you need in the way of motor and drive at techref.massmind.org/techref/io/steppers.htm#Estimating