Getting ready to purchase a CNC milling machine that uses a 3 HP 220 V (3 phase) motor. What type of convertor do I need?

I've done some reading and searching and it seems like a rotary phase convertor with some sort of voltage conditioning is preferred?

Can an electronic phase convertor work as well?

The milling machine uses stepper motors and the control cabinet uses 120V. The spindle has a variable dial on the front for speed selection (no changing belt positions). Is this the same as a VFD?

If a rotary convertor is the way to go, can you go too large? Someone local has a 20 hp rotary convertor he wants to get rid of...

Thanks for any help...