Código PHP:
<html>
<body onload="inittitle(9);">
<script type="text/javascript">
function inittitle(size){
var aux = setInterval(function() { efec(++size); }, 50);
setTimeout(function() { clearInterval(aux); }, 1000);
}
function efec(size){
document.getElementById('span').style.fontSize=size*10+'%';
}
</script>
<span id="span">aaaaaaaaaaaaaaaaaa</span>
</body>
</html>