Form won't submit when pressing enter key

I have a form created by this code (I don't know if it's important): if ($_POST["submit"]) { //do form stuff } else { echo "<html>"; echo "<head>"; echo "<title>Form</title>"; echo "</head>"; echo "<body>"; echo "<h3>Lookup Customer</h3>"; echo "Enter the customer's <u>home</u> phone number:<br/>"; echo "<form action=\"$PHP_SELF\" method=\"post\">"; echo "<input type=\"text\" name=\"phone\" size=\"10\"> "; echo "<input type=\"submit\" name=\"submit\" value=\"Search\">"; echo "</form>"; echo "</body>"; echo "</html>"; } After you fill out the only field, you HAVE to click the submit button to submit the form. If you press enter to submit the form it reloads the form and clears out the info that was entered. I can't figure out why this is happening and I need to make it submit using the enter key and I don't want to do something fancy with javascript at all. Please help Thanks, Sarah