Magento 2 – How to Call Custom Module Phtml File in CMS Page

Try this

custom file path(Based on your theme you can change it)

app/design/frontend/{Package}/{theme}/Magento_Theme/templates/html/test.phtml

calling in xml layout file

<block class="Magento\Framework\View\Element\Template" name="test_file" template="Magento_Theme::html/test.phtml"/>

calling in blocks and cms pages

{{block class="Magento\Framework\View\Element\Template" name="test_file" template="Magento_Theme::html/test.phtml"}}

calling in any phtml file

<?php include ($block->getTemplateFile('Magento_Theme::html/test.phtml')) ?>

OR
as before

<?php echo $this->getLayout()->createBlock("Magento\Framework\View\Element\Template")->setTemplate("Magento_Theme::html/test.phtml")->toHtml();?>

Your phtml is rendered by a block class.
You need to add this in your block class.

protected $pageFactory;
protected $brandPage;
public function __construct(
    ....
    \Magento\Cms\Model\PageFactory $pageFactory,
    ....
){
    ....
    $this->pageFactory = $pageFactory;
    ....
}

public function getBrandsPageContent()
{
    if (is_null($this->brandPage)) {
        $this->brandPage = $this->pageFactory->create();
        $this->brandPage->load('brand_list', 'identifier');
    }
    return $this->brandPage->getContent();
}

then in your phtml you just call echo $this->getBrandsPageContent()