Error with php field validation - php

Question

I have a form on a PHP page which adds a contact into a MySQL table.
But my validation refuses to work. I have edited it a few times but when I click Add New Contact button, it adds them even if some fields are empty.
I am still getting the grasp of PHP, but I am sure my mistake is missing something simple.
<?php
// Don't post the form until the submit button is pressed.
$requiredFields = array (
"name",
"email",
"extension",
"extension"
); // Add the 'name' for all required fields to this array
$errors = false;
if (isset ( $_POST ['Submit'] )) {
// Clean all inputs
array_walk ( $_POST, 'check_input' );
// Loop over requiredFields and output error if any are empty
foreach ( $requiredFields as $r ) {
if (strlen ( $_POST [$r] ) == 0) {
$errors = true;
break;
}
}
// Error/success check
if ($errors == true) {
echo 'Fields marked with a * are required';
} else {
// no errors
// ...
}
}
// check_input function
function check_input(&$data) {
$data = trim ( $data );
$data = stripslashes ( $data );
$data = htmlspecialchars ( $data, ENT_QUOTES );
return $data;
}
?>
<h2>Add Contact</h2>
<form name="form1" action="<?=$_SERVER['PHP_SELF'];?>?mode=added"
method="post">
<table class="tableStyleClassTwo">
<tr>
<td>Name:</td>
<td><div align="left">
<input type="text" name="name" />
</div></td>
</tr>
<tr>
<td>Phone:</td>
<td><div align="left">
<input type="text" name="phone" />
</div></td>
</tr>
<tr>
<td>Email:</td>
<td><div align="left">
<input type="text" name="email" />
</div></td>
</tr>
<tr>
<td>Extension:</td>
<td><div align="left">
<input type="text" name="extension" />
</div></td>
</tr>
<tr>
<td>Department:</td>
<td><select name="department">
<option value="ADMIN">ADMIN</option>
<option value="AFTER-SALES DIRECTOR">AFTER-SALES DIRECTOR</option>
<option value="ALPINE DEALER PRINCIPAL">ALPINE DEALER PRINCIPAL</option>
<option value="AUTO ARMOUR/AUTO ENHANCE - FITMENT CENTRE (Smash and Grab)">AUTO ARMOUR/AUTO ENHANCE - FITMENT CENTRE (Smash and Grab)</option>
<option value="BANDIT-VW">BANDIT-VW</option>
<option value="BOOKINGS VW">BOOKINGS VW</option>
<option value="DRIVEWAY/WASHBAYS">DRIVEWAY/WASHBAYS</option>
<option value="FINANCE AND INSURANCE">FINANCE AND INSURANCE</option>
<option value="IT DEPARTMENT">IT DEPARTMENT</option>
<option value="MARKETING DEPARTMENT">MARKETING DEPARTMENT</option>
<option value="MASTER CARS">MASTER CARS</option>
<option value="MAYOR OF PINETOWN">MAYOR OF PINETOWN</option>
<option value="NEW CAR PREP DEPARTMENT">NEW CAR PREP DEPARMENT</option>
<option value="NUMBER PLATES">NUMBER PLATES</option>
<option value="PANELBEATER - EASIFIX - CAR CARE">PANELBEATER - EASIFIX - CAR CARE</option>
<option value="PARTS">PARTS</option>
<option value="PARTS DISPATCH">PARTS DISPATCH</option>
<option value="PARTS TELESALES">PARTS TELLESALES</option>
<option value="USED CAR PREP AND ORDERS">USED CAR PREP AND ORDERS</option>
<option value="VW NEW CARS ADMIN AND STOCK CONTROL">VW NEW CARS ADMIN AND STOCK CONTROL</option>
<option value="VW NEW VEHICLE SHOWROOM">VW NEW VEHICLE SHOWROOM</option>
<option value="VW SERVICE ADVISORS">VW SERVICE ADVISORS</option>
<option value="VW WORKSHOP">VW WORKSHOP</option>
<option value="VW WORKSHOP FOREMEN">VW WORKSHOP FOREMEN</option>
<option value="WARRANTY & CLAIMS">WARRANTY & CLAIMS</option>
<option value="WORKSHOP DRIVERS">WORKSHOP DRIVERS</option>
</select></td>
</tr>
<tr>
<td colspan="2" align="centre">Back
| <input name="Submit" type="submit" id="Submit" value="Add New Contact" <?php if($disable ==1){?> disabled <?php } ?> />
</td>
</tr>
<input type="hidden" name="mode" value="added">
</table>
</form>
<?php
break;
//added a record
case 'added':
//first setup the vars
$name = $_POST['name'];
$phone = $_POST['phone'];
$email = $_POST['email'];
$extension = $_POST['extension'];
$department = $_POST['department'];
//then lets use'em
$sql = "INSERT INTO address (name, phone, email, extension, department) VALUES ('" . $name . "','" . $phone . "','" . $email . "','" . $extension . "','" . $department . "')";
//echo $sql;
//return;
mysql_query($sql);
//done take me back to the main page
header('location: ' . $_SERVER['PHP_SELF']);
break;