Why am I getting this message on my iPhone?

The messages are scam attempts, presented by criminals. Do not interact with the message or the sender. For information from Apple regarding such bogus messages, please read the information at the link below. Delete and report as spam.

Recognize and avoid social engineering schemes ... - Apple Support

They know nothing about your phone. The only thing they know is your phone number, which is easily obtained. If this is the first spam/phishing message you have received, then you should also know that it is not advised you call any phone number or click a link in a message and provide any personal information. That is how you become a victim of a phishing attempt. They can send out thousands of these and it just takes a small percentage of users to fall for them.

Because someone is trying to scam you. Delete it and move on.

Why?

Because someone you do not even know is trying to trick you into calling the number, so they can sell you useless software to fix a problem that never existed on your iPhone.

If you haven't seen other similar type messages like this, that is amazing. We all get scam attempts like this on a regular basis.

Delete the message and report as spam. NEVER call the number in a message like this.