How many phases are there in the menstrual cycle?

The menstrual cycle is divided into two distinct phases: follicular and luteal.

The follicular phase lasts until ovulation and begins on the first day of menstruation. During this stage, the uterine lining thickens and an ovarian follicle begins to mature. The follicle houses an egg, which is released during ovulation. 

The luteal phase begins after ovulation and lasts until the next menstrual cycle begins. The ruptured follicle transforms into the corpus luteum, which produces hormones to keep the uterine lining thickened. If the egg is not fertilized, the corpus luteum degenerates and hormone levels fall, causing menstruation to begin and the next menstrual cycle to begin.