Any PHPSpellCheck Spell-As-You-Type enabled textarea can be made "elastic" so that it grows vertically to match teh size of it's content.
<textarea name="spellfield" id="spellfield" cols="50" rows="20" style="height:auto" >
...
</textarea>
<?php
require "/phpspellcheck/include.php";
$mySpell = new SpellAsYouType();
$mySpell->InstallationPath = "/phpspellcheck/";
$mySpell->Fields = "ALL";
echo $mySpell->Activate();
?>