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 meters that support it. You can enable Energy+ at Settings > Energy+
Devices that support 3 phase measurements
Wi-Fi P1 meter on a SMR version 4 or higher smart meter
Wi-Fi 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)