constant messages to clean my phone of malicious viruses

Whatever websites or apps you're visiting when these phishing scam messages are received should be avoided. There are no malicious viruses for iPhone's which haven't been Jailbroken. No one can lock your phone remotely.

Read this about these types of scams --> Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

The only way is to ignore them.

You can go to Settings, Apps, Safari and clear all website data and history, as it could be a cookie.