You can use iTunes to make a full backup of your phone, make sure you enable encrypted backups to store health data and passwords. This won't include iOS itself, but you can download the ipsw file for iOS 11 and Apple usually keep signing the previous release for a day or two (sometimes a week IIRC) after releasing a new iOS. AFAIK there is no way at all to backup all of your phone including the iOS installation.
A