App for “cleaning” iPhone?

There are no known viruses for an iPhone which has not be jailbroken. As such, there is NO need to use any app, which purports to remove viruses from an iPhone. If you received a popup message suggesting your phone has viruses, it was a scam message, intended for you to buy tools/services you don't need for issues you don't have.

Read this as well --> Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

None. Even if the app was free, it would still not be worth the money.