A spontaneous organization of clock network emerges via communication among cellular circadian oscillators. The organization of clock phases is comparable to network memory in the sense that the pattern is retained and is plastic subject to the photoperiodic light condition and the developmental stage. This pattern of coordinated timing, which we call the phase organization, can be understood as encoded memory of a daylength. Both the mechanism and function of the phase organization remain unknown, but a simple and elegant mathematical description of its formation can be achieved if we allow “negative” coupling among phase oscillators.