Locked out of iphone

If the message on the screen says "Unavailable" or "Security Locked", you are going to lose all of the data on the phone during the reset / erase process.

Sorry, no way to avoid that.

You do have a recent backup of the phone, correct? You can restore the backup during the new set up process, so your phone will look just like it did before.

Or, does the phone say Activation Locked? That is a different can of worms.