I think it should be quite simple, the three phase is usually just for 3ph motors such as spindle etc.
If you scrap the transformer and bring in 240v 1ph and install a VFD for the 3ph motor, all the rest is most likely 1ph control and controller etc.
You may have a 1ph transformer in the enclosure for this.
You have to find out what else is 1ph on the machine and what voltage.
Do you have machine drawings?
What make/type of CNC control is fitted?
One down side is IF the largest motor is 7hp then you may not find a VFD for 240v 1ph input.
210/230 3ph is quite common.
That is a large machine for home use.
Max.