Form sending email on landing/refresh of website - php

Question

My form is sending a blank email (field data empty) to me every time i visit my site or refresh it.
I had a look at a few posts mentioning 'Post/Redirect/Get', but that confused me more than helped, and im not sure if it pertains to my exact issue.
This was a basic responsive form i found online and had to find the PHP to actually send the form data. (Changing it to suit my needs)
I'm hoping there's just an error i've missed somewhere but i cant seem to find it.
Any help would be greatly appreciated. Thanks in advance.
Here is the basic form (minus css):
PHP:
<?php
$name = $_POST['name'];
$email = $_POST['email'];
$phone = $_POST['phone'];
$message = $_POST['message'];
$formcontent=" From: $name \n Phone: $phone \n Email: $email \n Message: $message";
$recipient = "MY EMAIL HERE";
$subject = "Portfolio Contact Form";
$mailheader = "From: $email \r\n";
mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");
echo "Thank You!";
?>
HTML:
<form id="contact-form" action="/" method="post">
<h3>Say Hello!</h3>
<h4>Fill in the form below, and I'll get back to you as soon as i can. Thanks!</h4>
<div>
<label>
<span>Name: (required)</span>
<input placeholder="Please enter your name" type="text" name="name" tabindex="1" required autofocus>
</label>
</div>
<div>
<label>
<span>Email: (required)</span>
<input placeholder="Please enter your email address" type="text" name="email" tabindex="2" required>
</label>
</div>
<div>
<label>
<span>Telephone: (required)</span>
<input placeholder="Please enter your number" type="text" name="phone" tabindex="3" required>
</label>
</div>
<div>
<label>
<span>Message: (required)</span>
<textarea placeholder="Include all the details you can" type="text" name="message" tabindex="5" required></textarea>
</label>
</div>
<div>
<button name="submit" type="submit" id="contact-submit">Send Email</button>
</div>
</form>

Answer 1

use isset
<?php
if(isset($_POST['submit']))
{
$name = $_POST['name'];
$email = $_POST['email'];
$phone = $_POST['phone'];
$message = $_POST['message'];
$formcontent=" From: $name \n Phone: $phone \n Email: $email \n Message: $message";
$recipient = "MY EMAIL HERE";
$subject = "Portfolio Contact Form";
$mailheader = "From: $email \r\n";
mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");
echo "Thank You!";
}
?>
it will post your email only when it submitted by any ..

Answer 2

i have post this one for other in stackoverflow link code link
this is my code.let try , i wish it will help you
<?PHP
$email = $_POST["emailaddress"];
$to = "you#youremail.com";
$subject = "New Email Address for Mailing List";
$headers = "From: $email\n";
$message = "A visitor to your site has sent the following email address to be added to your mailing list.\n
Email Address: $email";
$user = "$email";
$usersubject = "Thank You";
$userheaders = "From: you#youremailaddress.com\n";
$usermessage = "Thank you for subscribing to our mailing list.";
mail($to,$subject,$message,$headers);
mail($user,$usersubject,$usermessage,$userheaders);
?>