The Vulture King has a set rotation, that is quite apparent when you are tanking him.
It is often hard to see these rotations when you are not the focus of the Tyrant; instead of you reacting to the Tyrants position, you influence the position when you're in focus.
When not the focus, you are just reacting to 'a reaction from a reaction' and with lag/distance you can often miss the visual cues provided that the tanker sees before you do and find the whole fight chaotic.
I've found that the VK will use 4 swings. If you successfully parry these swings, you will normally not be effected by a poison D.O.T.
After the 4th swing, the VK will position for a Frontal attack (yellow highlighted area of effect).
At this point, you move behind the Tyrant and can unleash a good DPS burst/heal chain.
If you attempt to attack the VK during the '4 swing' rotation, he will PARRY resulting in attackers being silenced. It is best to parry the VK 4 swings, then attack freely from behind while he is occupied with his frontal assault.
Hope this helps others who are not in a position to see the rotations.