Merhabalar, aşağıda ki kod probleminizi çözecektir ;

<?php
$iphone = stristr(@$_SERVER['HTTP_USER_AGENT'],"iPhone");
$android = stristr(@$_SERVER['HTTP_USER_AGENT'],"Android");
$webos = stristr(@$_SERVER['HTTP_USER_AGENT'],"webOS");
$bberry = stristr(@$_SERVER['HTTP_USER_AGENT'],"BlackBerry");
$ipod = stristr(@$_SERVER['HTTP_USER_AGENT'],"iPod");
if ($iphone || $android || $webos || $ipod || $bberry == true)
{
?>
</div>
<?php }else{?>
<div style="width:300px;position:fixed;top:500px;left: 10px;z-index:99999;font-size:12px;">
<a href="https://api.whatsapp.com/send?phone=TELNO" target="_blank">
<img style="width:50px;" src="https://demobul.net/images/whatsapp.png" alt="whatsapp">
</a>
</div>
<?php } ?>