How can I fix iPhone that says "iPhone Unavailable"?

By using these instructions:--> If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support

3 Options

Wait 8 hours and enter the correct passcode. No data loss this way.

Easiest for most users.......use a computer to erase the phone and set it up again If you forgot your iPhone passcode or your iPhone is disabled - Apple Support

Not as easy for most users.......but does not involve using a computer if your iPhone is running iOS 15.2 or higher If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support

With options 2 and 3, you can use your most recent backup to restore data back to the phone during the new setup.

I think you just typed the wrong passcode many times and your iPhone get locked