This is an important project milestone rather than a "phase" that requires specific work. The project has ended and a maintenance and support phase starts requiring those resources in place.
There may be some announcements to make at this time through the communication channels that were specified in the project plan.
Depending on the scope of the project, it may be useful to inform the wider SDMX community of such a project, particularly if there are experiences and tools that may be shared. Contact the SDMX.org webmaster and SDMX LinkedIn group for this.