In the US, to apply to medical school, you need a bachelor's degree. Any 4-year university should suffice.
During college study for and complete the MCAT. Devote an entire summer to studying for the MCAT and consider paying for a prep course if you can afford it.
My son used MCAT Complete 7-Book Subject Review 2019-2020: Online + Book + 3 Practice Tests (Kaplan Test Prep) Kaplan Test Prep
It was about $140 and he achieved his goal score.
Apply to medical schools during your last year of college.
Medical school takes 4 years to complete.
After medical school an OB/Gyn would complete a 4 year residency for additional training.
A PhD is not needed to become an ObGyn. You must earn either an MD (Doctor of Medicine) or a DO (Doctor of Osteopathy) degree. (Or the equivalent from a foreign medical school + certification by the Educational Commission for Foreign Trained Medical Graduates). One must also complete an ObGyn residency and pass licensing and board certification exam.