So cool that you are interested in chemistry! A doctoral degree follows a bachelor's degree so your first step would be graduating from college with a chemistry, or closely related, major. It would be great to get some chemistry research experience while in college too. In your senior year of college, you would apply to graduate school with the intent to pursue a PhD in chemistry. Probably the chemistry faculty at your college would help you with this application process. Once you are in a graduate program, typically you take classes for 1-2 years and then transition into full-time research working on experiments for your doctoral thesis. All in all a doctoral degree can take 4-6 years, a lot depends on your progress in the research portion. I hope that helps and good luck!
Pursuing a PhD is an exciting experience! I am glad you are considering it. To be competitive, you are recommended to have a good GPA (3.5 or higher) and independent research in a closely related field on your campus that you can carry over several terms. Such experience shows that you are curious and dedicated to research. Also, getting into a research summer program prior to graduation has a significant impact for your application. Always check the graduate programs and connect with the Director of the graduate program you are interested in. They will provide advice with regards to course work and other means that will help you become competitive for their program. I personally took a year off to work in a research laboratory to explore my interest in researxh and it was quite valuable. Keep up the good work and best of luck!
Please meet with a Faculty Advisor at your university regarding this matter.
Best of luck with your education, personal, and professional endeavors!