Doing PhD is good. But getting job under F1 visa, I think it would be a little bit difficult for PhDs. If you approach for teaching in any universities, it is fine and most of the international students who do PhD and still in F1 do the same. But if you are thinking of working in some organization, I do not think that it is easy for you to get job coz the question of your visa status will arise after your F1 expires. I do not mean that you should not apply for other organization besides universities, you should better do Masters and work for some period and wait for opportunity to come and grab to do PhD.