The G1, S, and G2 phases are critical stages within the cell cycle, collectively known as interphase. G1 (Gap 1) is a period of cell growth and preparation for DNA replication. The S phase (Synthesis) is where DNA replication occurs, resulting in two identical sets of chromosomes. G2 (Gap 2) involves further cell growth and preparation for mitosis. These phases ensure that the cell is ready to divide properly.