The first phase of your cycle is called the follicular phase. This begins on Day one of your cycle, which is the first full day of menstrual bleeding when the lining of the uterus starts to shed. When an egg isn't fertilized during the previous cycle, the body must shed the uterine lining to prepare for the next cycle.
For most women this lasts from 3 to 5 days, but can be more or less. Immediately following the shedding of the uterine lining, your body begins to prepare for the next phase in the cycle, the ovulatory phase.