mysql server port number

I've just made a database on mysql on my server. I want to connect to this via my website using php. This is the contents of my connections file:

$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'password';

$conn = mysql_connect($dbhost, $dbuser, $dbpass)
    or die('Error connecting to mysql');

$dbname = 'epub';
mysql_select_db($dbname);

I know what the username/passwords are, and I know the IP address of the server. What I'm just wondering is how do I know which port to use?