html contact form validatie code werkt nie goed!

<?php
// define variables and set to empty values
$nameErr = $emailErr = $phoneErr = "";
$name = $email = $phone = $message =$success="";

if ($_SERVER["REQUEST_METHOD"] == "POST") {
  if (empty($_POST["name"])) {
    $nameErr = "Name is required";
  } else {
    $name = test_input($_POST["name"]);
    // check if name only contains letters and whitespace
    if (!preg_match("/^[a-zA-Z-' ]*$/",$name)) {
      $nameErr = "Only letters and white space allowed";
    }
  }
  
  if (empty($_POST["email"])) {
    $emailErr = "Email is required";
  } else {
    $email = test_input($_POST["email"]);
    // check if e-mail address is well-formed
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
      $emailErr = "Invalid email format";
    }
  }
    
  if (empty($_POST["phone"])) {
    $phoneErr = "phone is required";
  } else {
    $phone = test_input($_POST["phone"]);
    // check if phone only contains Invalid phone number
    if(preg_match("/^[0-9]{3}-[0-9]{4}-[0-9]{4}$/", $phone)) {      
      $phoneError = "Invalid phone number";

    }
  }
}
	
	function test_input($data) {
  $data = trim($data);
  $data = stripslashes($data);
  $data = htmlspecialchars($data);
  return $data;
}

?>

<?php

if ($name_error=='' and $email_error=='' and $phone_error=='') {
		$message_body='';
		unset($_POST['submit']);
		foreach($POST as $key => $value) {
			$message_body .= "$key:$value\n";
			
		}	
		$to='[email protected]'
		$subject='Contact For Submit'
		if ($mail($to,$subject,$message)) {			
			
			$success="Message Sent,thank you for contacting us!" ;
			$name=$email=$phone=$message=''
		}
	
	}
	
?>

</php
if ($name_error=='' and $email_error=='' and $phone_error=='') {
		$message_body='';
		unset($_POST['submit']);
		foreach($POST as $key => $value) {
			$message_body .= "$key:$value\n";
			
		}
?>

<fieldset>
      <input placeholder="Your name" type="text" name="name" value="name" tabindex="1" autofocus=""></fieldset>
<fieldset>  <input placeholder="Your Email Address" type="text" name="email" value="$email" tabindex="2"></fieldset>
<fieldset>      <input placeholder="Your phone" type="text" name="phone" value="phone" tabindex="3"></fieldset>
<fieldset>
 <textarea placeholder="Type your Message Here...." type="text" name="message" value="message" tabindex="4"></textarea></fieldset>