How to add breadcrumbs on custom phtml page?

You can add breadcrumbs from your custom index controller action. Reference code is below.

<?php 

 
    public function IndexAction() {     
      $this->loadLayout();
      $this->getLayout()->getBlock("head")->setTitle($this->__("CB Magento Developer"));  /* add your page title */
            $breadcrumbs = $this->getLayout()->getBlock("breadcrumbs");
      $breadcrumbs->addCrumb("home", array(
                "label" => $this->__("Home Page"),
                "title" => $this->__("Home Page"),
                "link"  => Mage::getBaseUrl()
           ));

      $breadcrumbs->addCrumb("magento_developer", array(       /* add css class */
                "label" => $this->__("Magento Developer"),
                "title" => $this->__("Magento Developer")
           ));

      $this->renderLayout();

    }

?>