$_SERVER['PHP_SELF'] cannot POST the information of this page?

$_SERVER['PHP_SELF'] cannot POST the information on this page?

Please enter the ID number, if not, enter the ID number you want

<code><form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<input type="text" id="id" name="id" /><br />
<input type="submit" value="submit" name="submit"/></code>

$_POST['id']=$id;
echo $id;
?>
Can't I echo the text I just entered directly on this page? ?

Reply content:

$_SERVER['PHP_SELF'] cannot POST the information on this page?

Please enter the ID number, if not, enter the ID number you want

<code><form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<input type="text" id="id" name="id" /><br />
<input type="submit" value="submit" name="submit"/></code>

$_POST['id']=$id;
echo $id;
?>
Can't I echo the text I just entered directly on this page? ?

$_post is on the right, and the assignments are all wrong