Hello,
Anne from MyShoebox here! If you delete a photo from your phone's gallery your photo will remain safely backed up in MyShoebox. Just be sure that any photos have been uploaded in their original resolution to MyShoebox before you delete anything from your phone. Depending on your MyShoebox Sync Settings you may just have a preview photo backed up to MyShoebox (in Android this happens when you've selected "Data Saver" as your Sync Setting).
Cheers,
Anne
