# Phases

Phases are a flexible way to break a project into different work stages.

The Phase class is a subclass of [Project](/api/resource_management/openapi/projects), which is a subclass of [Assignable](/api/resource_management/openapi/assignables).

> **Note:** Every phase has a parent project; therefore, the `parent_id` for a phase is never `null`. A project's `parent_id` is always `null`.