iPhone backup to iTunes
iTunes backs up my iPhone SE but everything is listed as "Other".
iPhone SE, iOS 12
Reboot your device. Does Settings > General > iPhone Storage give a more reasonable breakdown? Try connecting to iTunes again, any better? See Recover your iTunes library from your iPod or iOS device - Apple Community if there is content on your device that isn't in your library, and wouldn't be included in an iOS device backup.
tt2