How to call a PHTML file within a CMS page Magento 2 ?

To call a phtml file in a cms page or cms static block:

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

If you know, where the block file(php file) for your phtml file resides, then you can use it as type.
Example: Suppose you want to call new.phtml file that resides in catalog/product folder, and you know that its corresponding Block file(php file) resides in Catalog/Product folder, then you can use:

{{block class="Magento\Framework\View\Element\Template" template="PackageName_ModuleName::catalog/new.phtml"}}