In most cases, a phase converter will have little or no effect on your bill. This is because the load will take exactly the same number of kilowatt-hours of electricity regardless of whether it is being registered on a three-phase or single-phase meter. Any change in your power bill will be caused not by the converter, but by the rate structure that the utility applies to single-phase power vs three-phase power.
In other words, if you are currently running single-phase power, you will see no difference in your bill running a phase converter. However, if you are currently running three-phase power (or are considering installing utility three-phase power), switching to single-phase with a phase converter could result in lower utility bills. For one, you'll be able to take advantage of the single-phase rate structure, which can often be lower than the three-phase rate. In addition, most three-phase rates include a demand charge, something rarely included in single-phase rates.