- preg_replace: documentation ( source)
<?php
foreach(array(
'localhost/web/category/finanzas/page/2/',
'localhost/web/category/finanzas/page/3/',
'localhost/web/category/finanzas/page/2000/',
'localhost/web/category/finanzas/'
) as $val) {
echo preg_replace('/page\/\d+\//', '', $val);
echo "\n";
}