"amps per phase", what is it, and what to look for?

Hi,
I'm specing out a Taig mill, cnc with servo's. I've seen "amps per
phase" listed as a spec for drives. How do you pick a driver with
respect to the amps per phase? As big as one can afford? Bigger is
better I assume, but to a point. At some level the amps per phase
would be "over-rated", i.e. more amps than one would ever need for
the given machine.

Regards,
Monte