The Equalizer is quite intelligent, and will inform your charger which phase has the lowest load. That phase will then be used for 1-phase charging. This is just one of the ways the Equalizer takes full advantage and utilizes your electricity to its fullest, most efficient potential.
Once the Equalizer has chosen the lowest loaded phase, it will not switch to another phase before the charging session ends. Once it starts again, the charger will then check again which phase to use.