Enabled PHP functions: fopen, fclose, fwrite

I just setup my first Ubuntu server and things were going smoothly until I realized that my tiny php script:

<?php
	// write email to a file
	if (isset($_POST['email'])) {
		$myfile = fopen("emails.txt", "a") or die("Unable to open file!");
		$txt = $_POST['email']."\n";
		fwrite($myfile, $txt);
		fclose($myfile);
	}
?>

was no longer working… I poked around the help boards, but couldn’t find any articles that were hand-holdy enough to get me a solution. Wondering if anyone can help!