Yep, like Grumbler and Mark mentioned: it's server side and you cannot really mix the two very well.
BUT: you can have the form pass a variable=value pair to home.php and inside home.php, you can look for certain values of the variable and trigger functions that way.
e.g.
in you HTML:
<form action="home.php" method=POST>
<input type="command" value="f1">
<input type=submit value="Call f1()">
</form>
in your PHP:
<?php
function f1() {
...
}
if($_POST['command'] == "f1") {
function f1();
}
?>
if you will have to call more than just f1, consider using a switch statement to compare multiple possible values for the $command variable.
-sridhar