I have created phtml file,
app/design/frontend/Smartwave/porto/Magento_Contact/templates/inquiry.phtml
<?php
/**
* Copyright © Magento, Inc. All rights reserved.
* See COPYING.txt for license details.
*/
// @codingStandardsIgnoreFile
/** @var \Magento\Contact\Block\ContactForm $block */
?>
<form>
<div class="form-group">
<label for="Full Name">Full Name:</label>
<input type="text" class="form-control" id="name">
</div>
<div class="form-group">
<label for="company name">Company Name:</label>
<input type="text" class="form-control" id="companyname">
</div>
<div class="form-group">
<label for="email id">Email Id:</label>
<input type="text" class="form-control" id="emailid">
</div>
<div class="form-group">
<label for="contact number">Contact Number:</label>
<input type="text" class="form-control" id="contactnumber">
</div>
<div class="form-group">
<label for="product name">Product Name:</label>
<input type="text" class="form-control" id="productname">
</div>
<div class="form-group">
<label for="comment">Comment:</label>
<textarea class="form-control" rows="5" id="comment"></textarea>
</div>
<button type="submit" class="btn btn-default">Submit</button>
</form>
</form>
and call this file in a static block in the backend
<p>{{store url="inquiry-page"}}</p>
{{block class="Magento\Framework\View\Element\Template" template="porto/Magento_Contact/inquiry.phtml"}}
but only <p>{{store url="inquiry-page"}}</p>
is working. Phtml block in not calling up