To clarify the terms circuit and phase:
In Germany, the power cable to the house connection has 5 wires: 3 phases L1, L2 and L3, each of which is shifted 120 degrees from each other, neutral conductor and earth. At the distribution box, the 3 phases are typically distributed evenly over the individual circuits, i.e., L1 on circuit 1, 4, 7, 10, etc., L2 on circuit 2, 5, 8, 11, etc., L3 on circuit 3, 6, 9, 12, etc. Each circuit has its own circuit breaker (or fuse) in the distribution box.
Each individual circuit has three wires, the phase L (230V, 50Hz), neutral and earth. Nowadays, every room, but also every larger consumer (such as washing machine, dishwasher, oven) should have its own electrical circuit.
To clarify the concept of the phase correct connection:
The sockets and power plugs are also significantly different from those in the US. The Schuko connectors commonly used in Germany (Schuko socket and Schuko plug) are symmetrical and therefore not polarity-proof, i.e., phase and neutral conductor are not firmly assigned. That's why many hi-fi manufacturers mark the phase on the power plug and refer to the phase correct connection in the manuals.