if someone insists in using 120 V voltage for spindles, of course you can do that if you stay within the capability of the domestic 120 V power supply circuits in USA. This is usually 20 or 30 A max. Therefore, a 2.2 kW spindle is prohibitive at 120 V, and this is also the reason why unserious chinese VFD sellers simply omit the input current rating on their nameplates and in their VFD manuals, because they want you to buy them despite of this.
The excellent Omron MX2 VFDs, that I can recommend, are nearly identical to Hitachi WJ200 VFDs, but the latter offer two models in the girly power class, for 0.4 kW and 0.75 kW spindles.
Note that 750 W on a spindle has nothing to do with 750 W on your trim router and cannot be compared at all. The router means this as electrical input AC power, which because of the poor efficiency of universal motors with carbon-brush motors say not much about the mechanical power, while spindles (induction motors) are required to be specified according to IEC 60034-1, which means the rating for the motor power in kW is not the electrical consumption power, but the mechanical power available at the shaft. Of course the electrical power is much higher, as calculated here for you. That means, a VFD that is rated “for 2.2 kW spindle”, with this, it means the mechanical power at the end of the shaft, and is in real able to draw over 4,5 kVA from your supply circuit, which means, you need a circuit able to supply 20 A if you have 230 V, and 40 A if you have 120 V (for a spindle rated as 2.2 kW).
It is less for a 1.5 kW or 0.75 kW spindle. 0.75 kW on a spindle is a lot, and the power is not delivered like on the hand trim router, but rather like shown here, so the change to a 0.75 kW spindle will bring you all the constant torque over a wide speed range, high efficiency, low noise and long life, that the router is unable to provide.
But one would ask, why take 120 V, when you have split-phase electricity in the U.S. which offers 240 V for air conditioners, table saws, etc., and then you have half the fuse and half the wire gauge on your spindle/VFD, as with 120 V.