Submit to same page with an anchor - php

Question

I am trying to understand how forms work , so far I understood that I could submit the form and refresh to the same page through
> action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>"
and then catch the errors or not have blank inputs.
However, let's say I have anchors in the page (sections in other words like #ContactUs) how could I refresh the page using action to get to that specific place instead of going back to top of page?
Thanks for all in advance
Here is part of the code:
<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
<h2>SEND US A MESSAGE!</h2>
<span>We'd be happy to hear from you.</span>
<input name="contactname" placeholder="Name" type="text" value="<?php echo $contactname;?>"/> <span class="error"> <?php echo $contactnameErr;?></span>
<input name="contactemail" placeholder="Email" type="text" value="<?php echo $contactemail;?>" /><span class="error"> <?php echo $contactemailErr;?></span>
<input name="contactphone" placeholder="Phone #" type="text" value="<?php echo $contactphone;?>" /><span class="error"> <?php echo $contactphoneErr;?></span>
<input name="contactsubject" placeholder="Subject" type="text" value="<?php echo $contactsubject;?>" /><span class="error"> <?php echo $contactsubjectErr;?></span>
<textarea name="contactmessage" placeholder="Message"><?php echo $contactmessage;?></textarea><span class="error"> <?php echo $contactmessageErr;?></span>
<input type="submit" name="submit" value="Send" class="contact-button" />
</form>

Answer 1

You should have a validation for it for example
<?php
if(isset($_POST['submit'])){
//then do something
header("Location: #contactus");
}
?>
So this way even if you load, it does not give you empty and does not ask you to resubmit

Answer 2

You can Use jQuery as i given below
<?php
if(isset($_POST['submit']))
{
//
//sql query and display
//
?>
<script>
$(function() {
$('html, body').animate({
scrollTop: $("#contactus").offset().top
}, 2000);
});
</script>
<?php
}
?>