Phthonos was actually a cool name - though very unfortunate. A mythological explanation
I noticed Mark answered but did not explain the mythology. A shame in my opinion, because Matt (the lore guy) does neat little mythological inspirations and such, and I think they would be appreciated more if they got more explanation. I'm a big nerd for this stuff.
Phthonos, post the opinion of Aristotle and his philosophy, is purely a negative force - jealousy of those who do not have something you do not. However, this was not a view shared by all of his contemporaries, and ancient Greek has a more nuanced view of him - as with the other ancient graecian gods, they are somewhat detached from human morality and have reasons to both worship and fear them.
The ancient Greek view of Phthonos (both the god and emotion) is more akin to spite - more specifically, especially of those who are in a station who do not deserve to be there.
So the name was essentially named as a spiteful force of nature that is dragging down the uppity Wardens (or their ships) back down to the level where they belong.
Unfortunately, the more Byzantine take on Phthonos makes for a much more comical look at the situation.