Simple bubbling method in PHP

It's a very basic thing. I feel that the code is not concise enough. I hope experts can guide me to modify it.
Reprinted from PHP interview questions: http://phpmst.com/

function BubbleSort($str){
 for($i=0;$i for ($ k=count($str)-2;$k>=$i;$k--){//Bubble this value forward;
 if($str[$k+1]<$str[$ k]){ //Change the less than sign to the greater than sign, which is to sort in descending order;
 $tmp=$str[$k+1];
 $str[$k+1]=$str[$k];
 $ str[$k]=$tmp;
 }
 }
 }
 return $str;
}
//The following is the test
$str=array(5,8,2,6,10,0,3,12, 11);
print_r(BubbleSort($str));
?>