<?php
class Form_DetailsForm extends Zend_Form
{
    public function init()
    {
    // ...
        $phone = new Zend_Form_Element_Text('phone');
        $phoneLabelExtra = $translate->_('deal511-extra');
        $labelText = sprintf("%s \n<br /><span class=\"label-description\">%s</span>",
            htmlspecialchars($translate->_('deal511')), htmlspecialchars($phoneLabelExtra)
        );
        Zend_Registry::get('fb')->info($labelText);
        $phone->setLabel($labelText)
            ->addFilters(array(
                'StringTrim',
                'HtmlEntities'
            ))
            ->addValidator('NotEmpty', true)
            ->setRequired(true)
            ->setOptions(array('class' => 'field-phone'));
        $labelDecorator = $phone->getDecorator('Label');
        $labelDecorator->setOption('escape', false);
        $this->addElement($phone);
    // ...
}
}