3 phase systems are supported in the basic app functionalities and will be shown as a combined total.
If you upgrade your app with Energy+ you can enable data logging for all 3 separate phases for devices that support this. You can enable Energy+ at Settings > Energy+
Devices that support 3 phase measurements
P1 meter on a smart meter with SMR version 4 or higher
kWh Meter 3-Phase
Enable 3-Phase graphs:
Settings > Graphs > 'Your graph' > Show phases in line graphs (if this option is not available, it is not supported by the smart meter)