Although there are single phase VFD's
http://www.anaconsystems.com/text/singleov.html
They have usually very severe limitations on some motors, especially at low rpm, and as HU said the recommended way is to switch to a 3 phase motor which will give you much better control at low rpm etc, also you mention it is a 400v VFD so you would not be able to use it for your 120v motor. It will require 400vac input.
If you are limited to single phase 120/230 the common solution is to obtain a 230 volt VFD that you can operate on single phase in, this will give 230v 3ph out to operate a 220/230v three phase motor.
Al