[ul][li]Assuming the phone is set to mount as an MTP device and not a drive-letter:
Try the latest beta version if you're not using it already. (The link is in my signature.) There was a fix related to Samsung's MTP implementation which might help (although it's not definite that it will).
I've also found that sometimes the MTP stack on the phone and/or the computer can get confused and not list anything, or show out-of-date listings. (I've seen it affect both Opus and Explorer, not always at the same time.) Rebooting the phone and fully exiting & restarting Opus usually helps. (Make sure the phone is unlocked when you then try to read the folder.)
Failing all else, try setting Preferences / Miscellaneous / Advanced: mtp_enable to False, which will make Opus use an embedded instance of Windows Explorer for MTP folders.[/li][/ul]