Yes, the two left most screws (P,N) are phase and neutral for the power supply. Internally, they’re completely isolated from the next 4 screws (N, L1, L2, L3) which are used for power measurements. It turns out that’s fairly critical in order to be able to calibrate it. But I guess it also means you can power the device from a different supply to the ones you are measuring (a UPS for example).
In that photo there is only one phase so you can see the brown wire loops from P to L1, L2 and L3 giving you an 18-channel single phase monitor. If you’ve got two phases, you can do a 12-channel / 6-channel split.