Hm....In KH1 I was able to handle most bosses after I got 2nd chance, leaf bracer and once more abilities but what level you have all three by varies. For Phantom and Kurt Zisa anywhere between 65 and 70 should be enough. I'd tackle Ice Titan at 70, Sephiroth at 100, and Xemnas anywhere between 90 to 100.
I only have a small slot every day it's fast enough for a video. TnT