[kirankn]

Working for Google/FB shouldn't be actual goals. The actual goal probably should be to do something interesting and making it big. So, even if you were to do the PhD, you might still be at crossroads figuring out what to do next. The startup, if whatever you said works, should give you enough to explore and understand your boundaries and in that process if you feel that you lack something that can only be fulfilled by a PhD, you can always do it later. You may not get such an opportunity again soon.