While Phoenix Dive always did area damage at both the start and end of its journey, it did not used to set the user on fire. It doesn't hurt to ask the developers if this is actually intended or a bug.
Honestly, Phoenix Dive already had enough drawbacks. You had to take special care that you were well away from the rest of your group when using it, as the launch would damage every ally around you. And landing amidst a pack of adversaries isn't exactly the safest situation to end up in either.
If setting the caster on fire is intentional (and I highly doubt it is), it seems like overkill on the penalties for what is essentially an alternative to Battering Ram. Yes, unlike Battering Ram it can more easily avoid elemental ground effects when moving from point A to B, but (unlike Battering Ram) it also isn't knocking down and damaging everything along its entire path.
Spoilers: As I'm certain your aware once you reach a certain point in the game Phoenix becomes: A self heal, a teleporter, and an AoE. None of these effects are game changing and I can see why, at lower levels, it's a pain in the ass but if you build your character with fire in mind it's actually a very nice power.
