How do I check for viruses in my iPhone?

Google has no idea if your phone has a virus. You have likely received a scam message that is trying to trick you into buying useless software that will do nothing to help your phone.......but it will lighten your wallet.

Ignore and delete the message and keep working.

Bob is right; the message you got is a scam and should be ignored. No web site has any ability to check any system for viruses, much less an iPhone. Most importantly, do not ever click on any link in such a popup or contact the "support" in the contact information provided. All those places will do is suck money out of you without being of any benefit and often will be very harmful.

Regards.

Google is a reputable company, they didn't send you that message, it came from a website you were visiting.