Here we will learn how to call custom phtml file on any cms page or add phtml in your custom cms page.

First, go to the admin section and open CMS page in which you want to add phtml file.
Go to the content section and add blow code.
Note: Replace package and module with your custom module.

{{block class="Magento\Framework\View\Element\Template" template="Package_Module::test.phtml"}}

Are you want to add external CSS in cms page?
You just need to put below code in cms page->design tab->layout section.

Afer save CMS page clear cache.