(Spoilers!) Help with an end game optional boss!

So I've made it to the King of the Storm fight and I can dodge almost every one of the dragon's attacks except for when he goes airborne and flames to the ground. No matter which way I try to dodge the flame always seems to track me. Any ideas on how to avoid it? I'm doing OK when I get to the Nameless King portion but I use so much health and Flasks due to that one move in the 1st phase that it's nearly impossible when I get there. I tried watching other people beat it but they either had summons (which I'm basically unable to get, fails every time I try) or they were doing more damage and somehow beat the phase without him doing that move.