It's really quite the opposite. Synthetic estrogen and progestin (a form of progesterone) in the pills travel through the bloodstream to the hypothalamus and the pituitary gland. The estrogen suppresses production of FSH in the pituitary gland so follicle maturation doesn't occur. Without a mature follicle, no egg is released and fertilization does not occur. Other than the 'morning after' pill and 'IUDs' there are very very very few post-fertilization, noninvasive methods of 'birth control'.
The phenomenon is called a "breakthrough ovulation" when an egg is released despite the Pill's suppression. It isn't rare, and when it happens the egg can be fertilized, i.e. conception takes place, but the fertilized egg cannot attach to the lining of the uterus, which sheds it because of the hormones. Thus, yes, it is an abortion, regardless of whether the unwitting mother knows it or not. That's the bad thing, they never know, all these times it has happened but the women never knew.
First off, the "morning-after pill" is just a higher dose of the same hormones found in regular BC pills.
Every package insert for every hormonal contraceptive (pills, patches, shots) on the market will tell you that it acts primarily by preventing ovulation but secondarily by changing the endometrium (the uterine lining) to prevent implantation of the fertilized ovum. If you don't believe me, read the package insert yourself.
Nobody can be consistently pro-life from conception through natural death and take the pill. It's simply not possible.