Нужны уникальные имена

while(...){
echo "<script>
                      function hideShowDiv(){
                         $('#show').slideToggle();
                      }
                   </script>";
                   echo "<div class = 'write_blog' tabindex = '0'>
                   <p class = 'write_in_blog' onclick = 'hideShowDiv();'>&nbsp&nbsp&nbsp$descript <f class = 'f'>&nbsp&nbsp($red: </f><a href = '$link_my_site' class = 'link_3'>$name $surname</a><f class='f'>&nbsp)</f></p>";
                   echo "<div class = 'write' id='show'><p class = 'text_5'>$write</p><hr class = 'line_3'>";
}

$i = 0;
while() {
$i++;
echo "...{$i}...";
}

$n = 0;
while(...){
$n++;
                   echo "<script>
                           function hideShowDiv(){
                           $('#show_$n').slideToggle();
                         }</script>
                   <div class = 'write_blog' onclick='hideShowDiv();' tabindex = '0'>
                   <p class = 'write_in_blog'>&nbsp&nbsp&nbsp$descript <f class = 'f'>&nbsp&nbsp($red: </f><a href = '$link_my_site' class = 'link_3'>$name $surname</a><f class='f'>&nbsp)</f></p>";
                   echo "<div class = 'write' id='show_$n'><p class = 'text_5'>$write</p><hr class = 'line_3'>";
}

$('#show_'.$n).slideToggle();

echo "<div class = 'write' id='show_{$n}'><p class = 'text_5'>{$write}</p><hr class = 'line_3'>";

$('#show_{$n}').slideToggle();

  echo "
      <script>
          function hideShowDiv(){
              $('#show_{$n}').slideToggle();
          }
      </script>
      <div class='write_blog' onclick='hideShowDiv();' tabindex='0'>
          <p class='write_in_blog'>
              &nbsp;&nbsp;&nbsp;{$descript}
              <f class='f'>&nbsp;&nbsp;( {$red}: </f>
              <a href='{$link_my_site}' class='link_3'>{$name} {$surname}</a>
              <f class='f'> )</f>
          </p>
          <div class='write' id='show_{$n}'><p class='text_5'>{$write}</p><hr class='line_3'>
  ";

<?php
//...
?><script>
function hideShowDiv(n){
    $('#show_' + n).slideToggle();
}
</script>
<?php
$n = 0;
while(...){
    $n++;
    echo "
        <div class='write_blog' onclick='hideShowDiv({$n});' tabindex='0'>
            <p class='write_in_blog'>
                &nbsp;&nbsp;&nbsp;{$descript}
                <f class='f'>&nbsp;&nbsp;( {$red}: </f>
                <a href='{$link_my_site}' class='link_3'>{$name} {$surname}</a>
                <f class='f'> )</f>
            </p>
            <div class='write' id='show_{$n}'>
              <p class='text_5'>{$write}</p>
              <hr class='line_3'>
            </div>
        </div>
    ";
}