Clearing icloud?

I’m planning on leaving my abusive relationship but one of my concerns is him having access to my iCloud. He bought me this phone but made me use his iCloud account.

He hasn’t gone through it yet but I know he will once I leave.

And I don’t want him having access calls/texts from the friends who are helping me escape, he will harass and threaten them. I don’t want any of my info, pictures, locations etc to remain on the iCloud for my safety along with my friend’s safety as well.

How do I go about removing everything off the iCloud and not just the phone itself?