The fourth phase is called the Luteal phase.
This phase lasts from ovulation until you get your next period. (Or, if we want to sound really smart, until menses!)
After the egg is released, the follicle it was in closes up and forms a pod called a corpus luteum. Meanwhile the egg is picked up by the Fallopian tube.
The corpus luteum releases a hormone called progesterone which causes glands in the womb (also known as uterus) to continue to build the lining. This lining is where a group of cells would attach and grow into a baby.
Did I just say baby?
I think I did. Woops. Camp Cranky forgot that part. A woman who has unprotected sex with a man can get pregnant when she has that fertile mucus. A sperm may fertilize an egg in the Fallopian tube. The cells divides and grow. If that group of cells attaches itself to the lining of the uterus, it means she is pregnant.
But if no sperm fertilizes that egg, it is reabsorbed into the body in 24 hours. About two weeks later, the lining of blood and tissue comes out of the vagina as your period.
So you're back to the beginning of your cycle again. The bleeding part. Your period. Menses. Get it?