Because I have had problems with this function to find out that there is no result to store in a variable, a short example how to use:
$font = imagepsloadfont( "/home/www/font/Arial.pfb" );
imagepsencodefont( $font, "/home/www/font/IsoLatin1.enc" );
afterwards you can use the resource $font in each other ps function like imagepstext() or imagepsbbox().