Which is added under phone configuration in Cisco Unified Communications Manager to add conference bridge resources to the phone?

Conference Resource List is not a standard configurable object in CUCM phone configuration; conference resources are managed through Media Resource Groups, not a dedicated resource list tied directly to a phone.

The Conference Bridge field in CUCM phone configuration allows an administrator to assign a specific conference bridge resource directly to a phone device, enabling that phone to host ad-hoc conferences using the designated hardware or software bridge resource.

A Media Resource Group is a logical grouping of media servers but is not directly added to a phone configuration page - it must first be placed inside a Media Resource Group List.

A Media Resource Group List (MRGL) is assigned at the device or device pool level to provide ordered access to media resources generally, but the question specifically asks about adding conference bridge resources directly on the phone configuration page.