Has my iPhone been hacked?

No, you haven’t been hacked. You are seeing one of millions of scam messages presented on the internet everyday. Close the offending page and avoid sites that are involved in such bogus advertising tactics.

Phony "tech support" / "ransomware" popup… - Apple Community

You have not been hacked. Apple will never send a message like this.

Someone is trying to trick you into buying useless software that will do absolutely nothing to help your phone. But, it will help to line the pockets of the scammers peddling this junk.