Get Phase Contents

List a workflow phase's direct children: doc folders, files, and forms filed directly at the phase root (not nested inside a folder). Works the same whether the phase belongs to a project or an opportunity. Each item carries a `type` field (`folder`, `file`, or `form`) telling you what it is. For `type: "folder"` items, call `GET /folders/{folder_id}/contents` with that folder's id to walk further in. Forms are ordinary files under the hood (`isForm: true` on the underlying file) that inherit their folder/phase placement, so they appear here rather than in a separate forms listing. Note: on this endpoint (and the folder-contents endpoint), the file's MIME/category label is named `fileType` instead of `type`, to avoid colliding with the folder/file/form discriminator. Phase instance ids come from the `type: "phase"` rows returned by `GET /projects/{project_id}/folders` or `GET /opportunities/{opportunity_id}/folders`.