Ground loops and earthing

[JAZZCNC]

Also, should a BOB be earthed (currently powered by an old phone charger with only two wires)? And should my PC earth be connected to the main earth point for everything else?

Ok common misunderstanding Here.? Your mixing up AC Earth and DC negative. They are very differant and should not be mixed up.
Your BOB will be DC and the Charger is converting AC to DC so your Phone charger is the only thing that should be connecting to EARTH not the BOB.(If charger as Earth often Don't)

Same goes with Other DC powered components IE: Drives etc. Only the Earth of the supplying Transformer should go to the Star EARTH point. Any DC Negatives should go to the (-) of the DC side of the supply.

One end of shields for things like Steppers, Limits, Homes etc go to the Star EARTH point. The spindle cable from VFD to spindle is the Only exception and can be connected at both ends and then it's best to run it back to Earth point on VFD. If the VFD is then powered from same AC supply in control box then run it's earth to the Star EARTH point.

Run Machine frame Earth back to Star EARTH point. Don't Earth the PC case and best to run it from separate supply to Control box.