Apple has a “files” app that lets you access your “home directory” on the phone. It def has “just there for storage” space. It’s literally the best way to access/delete some log files.
That directory doesn't work with Möbius Sync however. It gives an error when you try to set it as the local path for sync. Also, I can't figure out how to access that from Linux via ifuse: https://github.com/libimobiledevice/ifuse/issues/58