Simple html form does not submit from website

[dogrrific.com]

Hi,
In My Android smartphone, I found that although perfectly cross broswer my form (simple HTML) echoed by PHP
shows fine, let me enter content but does not submit
here is a simple one
echo"
<form action ='/promo/promo.php' method='post'>
<span class='emph'>Enter your Promo Code</span />
<input type='text' name='promo_code' />
<input type='submit' value='Submit' />
</form>";

what's going on?
thanks regards