If mobile browser then show less posts?

you can also use the php mobile class to detect the device and after that you can apply the str function of php.
of you can also use this code
$iphone = strpos($_SERVER[‘HTTP_USER_AGENT’],”iPhone”);
$android = strpos($_SERVER[‘HTTP_USER_AGENT’],”Android”);
$palmpre = strpos($_SERVER[‘HTTP_USER_AGENT’],”webOS”);
$berry = strpos($_SERVER[‘HTTP_USER_AGENT’],”BlackBerry”);
$ipod = strpos($_SERVER[‘HTTP_USER_AGENT’],”iPod”);

if ($iphone || $android || $palmpre || $ipod || $berry == true)
{ echo //your code ; }
else { echo //your code;}

I hope this can help you.