insert on same page

<?php
ob_start();
require 'connection.php';
if ($_SERVER["REQUEST_METHOD"] == "POST") 
{

$facebook = mysqli_real_escape_string($con, $_POST['facebook']);
$twitter = mysqli_real_escape_string($con, $_POST['twitter']);
$linkedin = mysqli_real_escape_string($con, $_POST['linkedin']);
$phone = mysqli_real_escape_string($con, $_POST['phone']);
$email = mysqli_real_escape_string($con, $_POST['email']);
$address = mysqli_real_escape_string($con, $_POST['address']);


$sql= "INSERT INTO contact (phone,email,facebook,twitter,linkedin,address) VALUES ('$phone','$email','$facebook','$twitter','$linkedin','$address')";

if(mysqli_query($con,$sql))
{
header("Location:a_edit_details.php");
}
else
{
echo "Error: " . $sql . "<br>" . mysqli_error($con);
}

}

?>


<form action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>" name="f11"  method="post" enctype="multipart/form-data" id="UploadForm">