how to backup me iphone when its freeze on the apple logo

You can't back up your phone if it is not starting up properly.

You would have had to already have a backup before that happens.

To solve the issue you are having:

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

But that is not a guaranteed solution, you might have to wipe your phone, or it might need service.

You can also:

Contact Apple for support and service - Apple Support

Good luck!