Yes, you can erase the currently mounted CineMag® with PHANTOMfuse. This will be done by the CineStation® in exactly the same way as the camera would. There is no need to re-erase it in the camera.
→ Click on the PHANTOMfuse icon of the macOS menu bar and select "Erase CineMag".
When you first erase a CineMag you will be asked to set a backup destination. PHANTOMfuse will then check if you have a copy off all the clips on the mag. As a last security measure it does only check for file names and file sizes. No checksums are verified.
If you set the backup destination to a very large backup volume it might take quite some time to run. To reset the path in such a case, please delete the backup_path setting via the following command:
rm ~/Library/Application\ Support/PHANTOMfuse/backup_path
You will then be prompted to set a new one on the next try.