I will try to formulate it as answer because i need to add the code.

Btw for this answer i assume your only problem is the sql error you have in your screenshot. The place you placed your print for the mysqlerror would never be reached btw because you have an mysql error and die() stops everything.

I think that the first answer is correct and you have to use $sort instead of $price. But if that does not work the code below should show you how to add extra debugging.

On a side note really use prepared statements or add some checking on sort (a white list or something)

This is the complete code (without validation) with some test code commented out. If it does not work after that you should uncomment the test code and run again and show the output. If things do work you can remove the commented lines i added.

  <h3>Mobilieji Telefonai</h3>
    <form method="post" action="">
     <select name="price">
    <option value="prioritetas">Atsitiktinis</option>
        <option value="kaina DESC">Kaina nuo mažiausios</option>
        <option value="kaina ASC">Kaina nuo didžiausios</option>
    </select>
    <input type="submit" name="orderPrice" value="orderPrice" />

 </form>
  </div>
  <?php


  if (!isset($_GET['startrow']) or !is_numeric($_GET['startrow'])) {
    $startrow = 0;
  } else {
    $startrow = (int)$_GET['startrow'];
  }
   $sort = @$_POST['price']; 

$query = "SELECT * FROM telefonai order by " . $sort . " LIMIT $startrow, 5";
//$query2 = "SELECT * FROM telefonai order by ". $price . " LIMIT $startrow, 5";
print $query;
//print $query2;

$fetch = mysql_query($query)or die(mysql_error());

$num=Mysql_num_rows($fetch);
    if($num>0)
    {
    echo "<table border=2  >";
    echo "<tr><td>Telefono pavadinimas</td><td>Nuotrauka<td>Kaina</td>     <td>Parduotuve</td><td>Nuoroda</td></tr>";
    for($i=0;$i<$num;$i++)
    {
    $row=mysql_fetch_row($fetch);
    echo "<tr>";
    echo"<td>$row[1]</td>";
    echo "<td>   <img src=\"{$row[5]}\"  width=75  height=75/>    </td>";
    echo"<td>$row[2] LT</td>";
    echo"<td>$row[3]</td>";
    echo "<td><a href=\"{$row[4]}\"><img  src=\"".base_url()."images/parduotuve.png\" /></a></td>";
    echo"</tr>";
    }
    echo"</table>";
    }
  echo '<a href="'.base_url().$this->uri->segment(1)."/".'?startrow='.     ($startrow+5).'">Sekantis</a>';
 $prev = $startrow - 5;
 if ($prev >= 0)
    echo '<a href="'.base_url().$this->uri->segment(1)."/".'?startrow='.$prev.'">    Buves</a>';
  ?>
  </form>
  </body>
  </html>
  <br>