My iPhone is telling me I have 27 viruses

Such messages are scams.

Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

Unless you have jailbroken your phone, you are victim of a phishing scam. I'm guessing you haven't jailbroken your phone, so don't click on the link and you'll be just fine. I see stedman provided a link for you to read about such scams.