Hello, Anina! I don't have a PhD in English myself, but some of my friends took that path. Most of them are teaching English or writing in high school, college, or graduate school, so in that sense it is a narrow career path -- and also an expensive one in terms of the schooling required. However, I would encourage you to think about a couple of things as you look for an answer to your question:
First, what do you want to do with a PhD in English? If you want to do creative writing, the best preparation is to write, whether for your school newspaper, in class, or in your spare time. Many people who want a career in writing novels, plays, etc. pursue an MFA (master's in fine arts) in creative writing. Some students who want to become lawyers major in English as an undergraduate, because learning how to write and speak helps them later on when they practice law.
If you want to teach, then yes, a PhD in English, comparative literature, or a language is probably where you want to go.
The second important question to ask is: why English? What do you truly want to study? "The social sciences" is actually a very broad subject area which can include the humanities (English, fine arts, history, etc.) as well as economics, sociology, psychology, and other disciplines. Many -- and I would argue all -- of these, while not specifically STEM careers, can involve a lot of math to be able to pull information and ideas from data that you collect. There are many, many exciting kinds of work that allow you to think about how human beings relate to each other -- which are really what the social sciences are all about.