(basic ?) Variable in iframe src error

Hi I'm trying to figure out why this isn't yielding any results. Any insight very much appreciated.

I have a .html page and eventually I will try to load this variable in from a database but for now I'm just taking it in baby steps.

my variable:

<?php
$spreadLink='https://docs.google.com/spreadsheet/embeddedform?formkey=dHlzZmxrX0tLenppNFhsQUxqSmEzZmc6MQ';
?>

my iframe:

 <iframe src="<?php echo $spreadLink; ?>" width="250" height="445px" frameborder="0" marginheight="0" marginwidth="0" scrolling="no">Loading...</iframe>

but when I go to view my html the iframe hasn't parsed the php and I get a 'page cannot be displayed' error.
Is there something I need to include in my html file? Something I need to do on my server side?