Leaving a job to pursue a PhD [D]

I have been working as a ML Engineer at a startup for 4 years and while the environment is very good and the pay is higher than average, I'm thinking whether I want to pursue a PhD. Working and doing the PhD at the same time is not really viable so this would also potentially mean quitting. What I don't like about the job is that I'm actually not doing any real data science and modeling. I guess I'm working on more modeling and scientific questions than most ML engineers but I'm barely scratching the surface of each problem and most problems are resolved with quick and data-driven methods. Rar