<?php
$veri = "li2_2;li2_3;li2_4;li2_5";

$li2_x = explode(";",$veri);

foreach($li2_x as $x)
{
   $x = explode("li2_", $x);
   
   foreach($x as $son)
   {
       echo $son . "<br />";
   }
}