So then in the HTML, just specify the value attribute of text areas. PHP isn't needed for this basic of an item.
If you want to fill it in based upon user input (like when they fill in their info, and you find something wrong with it (say phone number or email validation)) which is already sent, you'd have to do something like:
<?php
echo '<input type="text" name="something" value="' . (isset($_POST['something']) ? $_POST['something'] : 'my Default Value') . '" />';