Sounds like you did the right thing. Not that doing the right thing is always necessarily the best thing to do, as it probably would have been best just to leave it if nobody noticed. But the fact that you voluntarily told the invigilators about it should put you in a good position. If someone really was using their phone to cheat, how likely would they be to tell the invigilators that they had it? Plus, I doubt they would wait to tell you if you were in trouble. If you were going to be disqualified from the exam I think they probably would have taken you out of the hall straight away.
It's a shame that it made you lose focus for the rest of your exam, but this one exam is only a small part of the qualification, so as long as you do well on the other exams you should be fine. Also, you never know - you may have done better than you think! You can learn from this mistake. You'll probably sit a lot more exams in the future, and from now on you'll be even more likely to remember to hand your phone in, or not take it into the exam at all.