<?php

$arr = "post10
post9
post8
post7
post6
post5
post4
post3
post2
post1";

$arr = explode("\n",$arr);

print_r(array_reverse($arr));

?>

Array
(
    [0] => post1
    [1] => post2
    [2] => post3
    [3] => post4
    [4] => post5
    [5] => post6
    [6] => post7
    [7] => post8
    [8] => post9
    [9] => post10
)