how to save my data in situation of iphone unavilable

It's too late now to save the data on the iPhone. Hopefully you have a recent backup of the iPhone.

If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

Then, you have already lost all of the data on the phone and you will need to start all over again to manually install apps, etc.

For the future.......backups have to be made......before.....disasters occur.