These are intended for where you are connecting to a 3-wire, single phase 208V service or feeder, which is rare. I'm sure they would work in a small system if connected them to one phase of a three phase system with the Envoy connected to the same phase. But you wouldn't want to do that at scale, the utility probably wouldn't like the unbalanced output.
Enphase has other 3-phase micros in the IQ8 series and a different 3-phase Envoy (aka Gateway) and evidently they want to sell those and will not support these in a 3-phase system.
The IQ8 series mostly won't do that anymore.