Cell cycle has two main phases:
Interphase (I-phase) is the longest and metabolically active phase which has three phases, gap-1 (G1), S and gap-2 (G2).
Division or M-phase, where actual mitosis (or meiosis) takes place.
S phase:
Also called the invisible phase.
The DNA replication takes place at this phase of interphase.
The 2C DNA content of a cell becomes 4C at the end of S-phase.
There is no change in the ploidy level.