I have a notice that my phone has a virus, is this true, and how do I fix it

This is usually a scam technique that certain websites use inorder to get you to download a certain app or call them, from there they will try carry out one of many scams.

To get rid of that page that says you have a virus, you can simply close the tab, assuming your using Safari, click the two overlapping squares in the bottom right of the browser. From here you can click the little 'x' in the top left corner of each tab or swipe each tab to the left to close it. You only need to close the fake virus message at this stage but you may chose to close others such as the tab for the website that may have opened this tab or any addition tabs you no longer need open.

No matter how this message appeared, it's fake.