Skype for Business Online Plan 2 is being retired from sale as of July 1, 2019. If you are using any of these licences, you will receive an Office 365 message centre message. When your SfB Online Plan 2’s expire at the end of your current term, in order to have continued access to these features, you’ll have to switch to a different plan.
SfB Online Plan 2 was an Office 365 SKU which just included the Skype for Business Online core service, not an Office client (users could use the SfB Basic client free) or a bundle of other services. It has been pretty clear for some time Microsoft are moving away from selling individual Office 365 services in favour of bundles.
Sometimes people would use these to licence room systems (adding Microsoft Phone System and a Calling Plan), rather than buying a more expensive E3 or E5 licence which includes features not needed by a room system. Microsoft now have a specific licence for room systems.