the problem is, most of the time, you will receive less income while doing pHD compared to working. this is fine with you are young and fresh (age 20ish); to return to do a pHD after several years of work means you will be effectively taking a (sometimes massive) paycut.

so you have the willpower to do it? can you do it with the obligations and responsibilities you have when you are in your 30s (wife, kids, loans, etc)