I don't know too much about international universities but the impression I always get from those doing PhDs at not-so-great UK ones is that really it doesn't matter that much at all. The rankings in the league tables are normally based on statistics from undergraduates and sometimes refer mainly to the teaching/study resources that as a PhD student you won't be dependent on. Where it's so self directed it's much more down to the work and research you do under the *guidance* of the university. Having said that, if this guidance or the supervision you're receiving is substandard this might affect the kind of work you produce, but ultimately, if you still manage to pass your PhD no-ones going to turn their nose up at that, irrespective of the university you got it from. Bottom line is if you're feeling OK about the level of support you're getting and it's literally just the perception of the university that's bothering you, I really don't think you should worry - it's only if you feel that the university isn't that great based on what they're providing for you that it could be an issue. That's my opinion anyway!