Would it be unethical to take a full time job and quit 8 months later if I get accepted for a PhD program?
It wouldn't be unethical for your boss to fire you 8 months after you take the job, if he wanted to. Labor is an exchange you and your employer enter into voluntarily. So, you shouldn't feel bad quitting after 8 months if you want to. It's not an ethical problem at all. It is more plausible to think there might be a personal problem if this is a small industry that you would plan to re-enter after finishing the degree. Don't tell your boss up front that you might quit in 8 months, that isn't any of his business. If you do accept an offer to do a phd somewhere, then you should tell him promptly, just as a matter of courtesy. This is to allow the company adequate time to find a replacement.