ESTNN writes: “In Classic, we saw Blizzard match the release patch release of Vanilla content with a phase of release for Classic. While we saw a few things altered, such as BG releases and the honor system, for the most part, each phase was tied to a content patch. For TBC, however, Blizzard looks set to change that, especially for phase 1 and 2.”
Source: N4G PC TBC Classic Raid And Arena Content Release Timeline, Phase 1 Through 5