The circulator is one of the crucial devices in quantum networks and quantum simulations. We propose a four-port single-photon circulator based on a waveguide quantum electrodynamics system, where a driven $\mathrm{\Lambda }$-type giant atom is coupled to two coupled-resonator waveguides. We find that the phase difference between the atom and the upper (lower) waveguide can control the crossover between reciprocal and nonreciprocal photon transmission in the respective waveguide. Here, the phase difference refers to the relative phase carried by these coupling constants. Under specific phase conditions, the system exhibits multiple circulation modes, including cross-type circulation as well as fully unidirectional clockwise or counterclockwise photon transport. Meanwhile, the frequency position of the photon circulation can be controlled by adjusting the external driving frequency. This discovery introduces a control dimension for designing reconfigurable quantum photonic devices.

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• Quantum information theory