The cell cycle is divided into interphase and M phase (mitotic phase). The interphase is divided into three phases: G1 (gap 1) phase, S phase, and G2 (gap 2) phase. After G2 phase cell enters M phase, in which actual division of nucleus and cytoplasm takes place.
After division, newly daughter cells either enter to G0 (resting phase) or to G1 phase. Cells that enter to G1 phase are metabolically active and prepare for next round of division.
Thus, the correct option to be filled in the blank is 'G1 phase.'
