Define a release phase

You can define a phase from the Release form. Release Phases use the same fields as other Planned Tasks in the Planned Task plug-in

From the Release form, use the Release Phases related list.

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Release Phases are not used with the SDLC and SDLC - Scrum plug-ins. With SDLC - Scrum, phases are replaced by Sprints, which use the same fields as other Planned Tasks.