pop up on website

I got a similar "pop up" from that website using Safari on a Mac:

It's just as bogus. Ignore it, and all such things.

The Internet is a target-rich environment for scams. Consider not patronizing that website, and telling them why they lost your business. Perhaps they will be more circumspect regarding the advertising services they choose to host.

Phony "tech support" / "ransomware" popups and web pages - Apple Community

You do not have a virus. The message you saw came from the website you were visiting and is a form of advertisement that the website owner is paid for. Closing Safari and opening again will always return you to the same site as that is what it is supposed to do. You just need to navigate to a different website.

By the way there is no website that can perform any scan on your phone. The same is true for any app on the phone, as there is no access to the file structure to perform any type of scan. That is also why it is not possible for a website to install a virus.