Magento 2.4.4 Register Deprecated – How to Handle

Add Telephone to customer registration,customer edit page etc. run following setup script from magento root.

<?php
require_once('app/Mage.php'); 
umask(0);
Mage::app();


$installer = new Mage_Customer_Model_Entity_Setup('core_setup');

$installer->startSetup();

$vCustomerEntityType = $installer->getEntityTypeId('customer');
$vCustAttributeSetId = $installer->getDefaultAttributeSetId($vCustomerEntityType);
$vCustAttributeGroupId = $installer->getDefaultAttributeGroupId($vCustomerEntityType, $vCustAttributeSetId);

$installer->addAttribute('customer', 'cust_telephone', array(
        'label' => 'Customer Telephone',
        'input' => 'text',
        'type'  => 'varchar',
        'forms' => array('customer_account_edit','customer_account_create','adminhtml_customer','checkout_register'),
        'required' => 0,
        'user_defined' => 1,
));

$installer->addAttributeToGroup($vCustomerEntityType, $vCustAttributeSetId, $vCustAttributeGroupId, 'mobile', 0);

$oAttribute = Mage::getSingleton('eav/config')->getAttribute('customer', 'cust_telephone');
$oAttribute->setData('used_in_forms', array('customer_account_edit','customer_account_create','adminhtml_customer','checkout_register'));
$oAttribute->save();

$installer->endSetup();
?>

Run this Script, it will add attribute "cust_telephone" and now you can use this attribute in the register form, like this

<li class="fields">
    <div class="field">
        <label><em>*</em><?php echo $this->__('Customer Telephone') ?></label>
        <div class="input-box">
            <input type="text" name="cust_telephone" value="<?php echo $this->escapeHtml($this->getFormData()->getCust_Telephone()) ?>" title="<?php echo $this->__('Customer Telephone') ?>" class="input-text" />
        </div>
    </div>
</li>

the code is tested, will work 100% ;)

Alternative solution:

Delete: use Magento\Framework\App\TemplateTypesInterface;

Change TemplateTypesInterface::TYPE_HTML to self::TYPE_HTML

  <?php
    declare(strict_types=1);
    namespace Vendor\Module\Model;
    use Magento\Framework\Setup\Patch\DataPatchInterface;
    use Magento\Framework\Setup\Patch\PatchRevertableInterface;

    class InstallerBase implements DataPatchInterface, PatchRevertableInterface
    {
    ...
    
        public function __construct(
            ...
        ) {
            ...
        }
    
        public function save($subjectHTML)
        {
    
            $template->load($templateName, 'template_code');
            $template->setTemplateSubject($subjectHTML)
                   ...
                    ->setTemplateType(self::TYPE_HTML);
    
            return $template->save();
        }