NTT DOCOMO researchers discuss 3GPP’s 5G radio standardization process in the March 2017 issue of NTT Technical Review.
It explains the phasing of 5G radio development. Phase 2 is the end of the current concentration of activity due for completion in late 2019. That specification is intended to meet ITU’s IMT-2020 performance requirements. Phase 1 is for early commercial deployment. Before Phase 1 is done a third mode (called non-standalone, which is explained) will be culled for even earlier commercial deployment. (They also refer to Phase 1 and Phase 2 as 5G and 5G+, respectively.)