"But then, at the time of the councils, vast tracts of Western Europe were still 'barbarian lands'. Would the Phillipines then be under the Patriarch of Constantinople?"
Well to hear the EP justify his claim to jurisdiction in the Americas, you'd think so. Other Orthodox jurisdictions don't agree with that. I think if reunion ever comes, the hierarchs will have to work this one out and I suspect it will mean a change in the ancient jurisdictional rules since it is highly unlikely that any of us are going to be willing to give up our Rites if we live in what might have been anciently considered some other patriarch's territory. How this will work out I have no idea. Maybe those areas which were ancient territories will stay the same and the "new lands" in something of a free for all like it is now, but the Catholics in Greece and Russia and the Orthodox in France or England might not like that.