how to call a PHTML file within a CMS page Magento

View the source of your webpage and scroll to the bottom to see a php error.

form-top.phtml gets called but there is a php error inside which fails. The error might happen in an invisible div that's why you don't see it the normal way.

Replace your line with following code

{{block class="Magento\Framework\View\Element\Template" template="catalog/product/form-top.phtml"}}