How do I back up my iPhone to a flash drive? I know it's possible, I just don't exactly know how to do it.

Once you complete your iphone backup in itune. Just browse through macintosh>Users>choose user>library>application support >mobileSync>Backup. In backup folder you will find the backup file(folder) just copy file and paste in external hard drive or pen drive. Whenever you want to restore the backup just copy from hard drive and paste to same location where you copied earlier (mobileSync>Backup)

Check below link for step by step procedure

https://www.macgeniustricks.com/2016/10/14/take-iphone-ipad-backup-pendrive/

The iPhone backups are saved on the Users/user_name/Application Support/MobileSync/Backup folder. You can create a symlink that points that folder to your external flash drive, but those backups files are pretty big so iTunes may take longer to create those files in a flash drive.

Symlinks are created using the command ln -s, and it may look something like:

ln -s /Volumes/your_flash_drive_name_here /Volumes/your_hdd_name_here/Users/your_user_name_here/Library/Application Support/MobileSync/Backup

You can also find applications that make symlinks creaton easier.

you can directly backup your iphone into an external drive. for windows 7 user, the backup will be auto stored in:C:\Users\USERNAME\AppData\Roaming\Apple Computer\MobileSync\Backup

what i can think of is u try to find another pc which have itunes installed, u can try backup there without doing any sync, copy the backup file into ur thumb drive and keep since ur current computer is already full.

As a reminder, the backup in itunes doesnt contain ur apps/music/synced photos/videos 😉

if you have icloud set up then your backing up to iclould automaticly when you charge your phone as long as you have wifi, (using ios 5 or later). if you have never pluged up the phone to your computer, you need to install itunes for windows 7 (64 or 32 bit [which ever one you have]). plug up you phone and it will back it up and sync your phone to your computer.

I know this dont answer your question but if your new to iphone it will help.

In case you didn't notice, the post you replied to will be 6 years old in December. Hopefully they figured out something back then.