I think my IPhone has been hacked. What do I do?

As Bob Timmons pointed out, you do not have to worry about your phone being hacked, as this is not possible on an iPhone that is not jailbroken and you have not given out your passcode/password.

Just do not respond or tap a link in the message asking for any personal information. The message is looking for information from you, as there is no warning from your iPhone or Apple that would come up saying your phone has been hacked.

This is a common scam message that is trying to trick you into buying useless software that will do nothing to help your phone......or worse, providing personal information about yourself.

Do NOT open any of the links in a message like this unless you want to let the scammers know how to contact you in the future.

Delete the message and the others like it that you will see in the future.

How do you know that your phone has been hacked?

Tap Settings, then tap (Your Name) near the top of the screen

Look at the list of devices

If you see a device that you do not recognize, you may have an uninvited guest

But, as you will see......you don't.

Your phone has NOT been hacked unless you unlocked it and then let someone else use it for an hour or so.

Why do you think your phone has been hacked?

Are there other devices using your Apple ID that you don't recognize?

Here’s some additional guidance→Avoid phishing emails, fake ‘virus‘ alerts, phony support calls, and other scams

A few things to consider, one of them is check and 'clear history and cookies' from Safari iOS.

Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch - Apple Support

//support.apple.com/en-us/HT201265

"Learn how to delete your history, cookies, and cache in Settings."

Some adequate ideas are presented in this official Support article.

[PS: check 'google accounts' security settings, if you've gmail, etc.]