echo'
<form method="post">
<h3 class="title-h3">Информация для доставки:</h3>
<ul id="info-order">
<li><label for="order_fio">*ФИО</label><input type="text" name="order_fio" id="order_fio" value="'.$_SESSION["order_fio"].'" /><span class="order_span_style">Пример: Иванов Иван Иванович</span></li>
<li><label for="order_email">*E-mail</label><input type="text" name="order_email" id="order_email" value="'.$_SESSION["order_email"].'" /><span class="order_span_style">Пример: ivanov_ivan@gmail.com</span></li>
<li><label for="order_phone">*Номер телефона</label><input type="text" name="order_phone" id="order_phone" value="'.$_SESSION["order_phone"].'" /><span class="order_span_style">Пример: +38 095 512 0808</span></li>
<li><label class="order_label_style" for="order_address">*Город и отделение <br />Новой почты </label><input type="text" name="order_address" id="order_address" value="'.$_SESSION["order_address"].'" /><span class="order_span_style">Пример: г.Киев Отделение №1 </span></li>
</ul>
';
echo'
<li><label class="order_label_style" for="order_note">Примечание</label><textarea name="order_note">'.$_SESSION["order_note"].'</textarea><span class="order_span_style">Уточните информацию о заказе.<br /> <br /> Например, удобное время для звонка <br /> нашего менеджера</span></li>
</ul>
<p align="right"><input type="submit" name="submitdata" id="confirm-button-next" value="Далее" /></p>
</form>
';
<?php
// тут php
?>
<form action='action.php' method='post'>
<label class="order_label_style" for="order_address">*Город и отделение <br />Новой почты </label>
<input type="text" name="order_address" id="order_address" value="<?= $_SESSION["order_address"] ?>" />
<span class="order_span_style">Пример: г.Киев Отделение №1 </span>
</form>
<?php
// тут php
?>
function checkParams() {
var fio = $('#fio').val();
var email = $('#email').val();
var phone = $('#phone').val();
if(fio.length != 0 && email.length != 0 && phone.length != 0) {
$('#submit').removeAttr('disabled');
} else {
$('#submit').attr('disabled', 'disabled');
}
}
<input id='fio' onkeyup='checkParams()' />
<!-- остальные поля формы -->
<input type='button' id='submit' value='ОТПРАВИТЬ' disabled>