It is possible to blacklist website URLs from the GSFE Admin Console to specific User Sub-Organizations
Blacklisting is unavailable by device since the setting is only available for users in a sub-organization. If the setting was device based, users who require access to the site will be unable to access it on that device.
This policy is user-based to apply to any computer the end-user is logged in to.
Link to GSFE Admin Console: https://admin.google.com/ac/home
It might take a little while to be available if it is grayed out.
Under Content >> URL Blocking, you can add URLs to the URL blacklist.
To quickly find it, do a quick page search for: blacklist