3ph soft starter for 1ph motor

No. Use a variable speed drive instead.

A 3Ph VFD (or soft starter) will not run a 1Ph motor.

These are two different animals. The 1 phase motor typically has start and run windings controlled by a centrifugal switch. When the motor approaches running speed the switch will transfer to the run mode. If the motor does not go into run the winding can be damaged. Typically shaded pole motors are not used a the 4 kw level.

As metioned in another post the VFD will work for speed control on three phase motors and can be programmed to prevent damage of the 3 phase motor for your application.

First of all, you should know that soft startor is not equal to a VFD, so

the soft startor cannt control your motor speed. If you vary your

motor's speed you would use a VFD or inverter. Which can change

voltage and frequency simultaneously from starting to working peroid depending on motor's work situation. Whereas most of soft startor can only offer a ramp voltage at the start step.
if your starter is a simple designed one, you can use it for your motor starting. but if its a resonable designed one. the starter will refuse to work for you.
if you insist on to use it. there is a way to run, ie you use a scott transfermer as a medium.