How can I include a phtml file in Magento2 using block type="core/template"?

Try this

{{block class="Magento\Framework\View\Element\Template" name="BlockName" template="Magento_Blank::PathOftemplate/About.phtml"}}

In magento 2, Magento\Framework\View\Element\Template eq to core/template

in cms page i used below code its working fine

<p>{{block class="Sugarcode\Test\Block\Test" name="BlockName" template="Sugarcode_Test::test.phtml"}}</p>

Sugarcode\Test\Block\Test:- my block or else you can use "Magento\Framework\View\Element\Template"
Sugarcode_Test::test.phtml:- app\code\Sugarcode\Test\view\frontend\templates\test.phtml (template file )