Final answer:
In Phase 3, rotation 4 against Zulrah's green form in the video game, you should change your combat style to Ranged to effectively damage it.
Step-by-step explanation:
The question pertains to a specific scenario in the boss fight against Zulrah in the video game. When you find yourself in Phase 3, rotation 4 with Zulrah appearing green at the top, the best course of action is c) Change combat style. The green form of Zulrah is most vulnerable to Ranged attacks, so switching your combat style to Ranged, if you haven't already, will optimize your damage. Additionally, always be attentive to Zulrah's attack patterns since it might necessitate switching protection prayers or using healing items accordingly, but based on the brief context provided, changing combat style is the priority.