When using the mobile app, I'd like to choose whether images are saved to the gallery to prevent my phone gallery from filling up.

This is generally not an issue on Android, as I can choose if the individual folder is backed up or not. On iOS, there appears to be no way to exclude a gallery folder from iCloud backup.

The phone gallery filling up with images is more of an issue if I'm using my personal phone to carry out surveying - since I generally don't want work-related photos being saved to my personal phone gallery.