One of the many challenging things with growing up is learning how to make choices and set priorities. To be completely frank with you - you cannot have a serious acting career and work on the Ph.D. at the same time. One will have to take priority and the other will suffer because of it.
So why do you want to be an actress? I ask because many people have very unrealistic ideas of what is involved in attempting a professional acting career. It's not just going to a bunch of open auditions hoping to get "disoovered" or something. For most professional work you have to be invited to audition, usually through an agent. And you can't just hire an agent, it's more like they choose you. To attempt a professional acting career you're basically starting and running your own business where you are the product being marketed and sold. You need to understand the casting process (agents, breakdowns, casting directors); legal issues (contracts, unions, taxes); marketing (head shots, resumes, show reel, website, social media) and networking. A serious acting career requires a HUGE investment of time, effort, and money. It's not something that can be done on the side while you work on a Ph.D. The demands of a Ph.D. are not flexible enough to allow you to go on last-minute auditions or take weeks/months off to act in a project and producers/directors are not going to rearrange their scheduling to fit your academic schedule.
And if you are serious about an acting career, why do you need a Ph.D. in microbiology? It's not going to help you with an acting career. When attempting a professional acting career, it's important you are able to support yourself with an "along side" job that gives you the flexibility to put your acting career first. Being a researcher does not give you that flexibility.
You can certainly try some acting on the side while you work on your Ph.D. Maybe do a role in a community theater production or work on a student film if you can find people willing to cast you. But otherwise, you're going to have to do some research to understand the realities of attempting an acting career and what that involves and then do some self-examination as to how you personally are going to choose to define "success" and what your priorities are in your life.
A professional actor married to a Ph.D. neuroscience. I know what is involved with both careers.