User is trying to run the Project List report and wants to hide the phases under the projects to keep the report from becoming too long. However, in the Customize Report > Options tab, Core does not allow selecting Yes for the option Hide Phases.
This can happen if the option Group By is set to Project. Because the phases in Core are projects too, the Hide Phases option is irrelevant when you are grouping by project. To be able to hide the phases, you need to first select Master Project from the Group By drop-down and then you can select Yes for Hide Phases. Check the Core Help for more on customizing and running reports.