Send Data from Controller to PHTML – Magento 1 Guide

--We can use \Magento\Framework\Registry in your Block or Controller.

/**
 * Core registry
 *
 * @var \Magento\Framework\Registry
 */
protected $_coreRegistry = null;

...
$this->_coreRegistry = $registry;
...
$this->_coreRegistry->register('voucherNumber', $voucherNumber);

//We can get
$this->_coreRegistry->registry('voucherNumber');

--After loading layout, get the block and set values in Controller.

/**
 * @var \Magento\Framework\App\ViewInterface $_view
 */


/**
 * @return void
 */
public function execute()
{
    $voucherNumber = 24566;
    $this->_view->loadLayout();

    $block = $this->_view->getLayout()->getBlock('your_block_name');
    if($block) {
        $block->setVoucherNumber($voucherNumber);
    }
    $this->_view->renderLayout();
}

--We can use setData() or getData() in our Block.

  //In your Block:
  public function getVoucherNumber()
  {
        if (!$this->hasData('voucherNumber')) {

            $this->setData('voucherNumber', $voucherNumber);
     }
     return $this->getData('voucherNumber');
  }

 //In your template:
 <?php $voucherNumber = $block->getVoucherNumber();?>

Sample: Pass model object via controller.

<?php

namespace Vendor\Module\Controller\Test;

class Index extends \Magento\Framework\App\Action\Action
{
    /**
     * @var \Magento\Framework\Registry
     */
    protected $_coreRegistry;
    /**
     * @var \Magento\Framework\Controller\ResultFactory
     */
    protected $_resultPageFactory;

    public function __construct(
        \Magento\Framework\App\Action\Context $context,
        \Magento\Framework\View\Result\PageFactory $pageFactory,
        \Magento\Framework\Registry $coreRegistry
    )
    {
        $this->_coreRegistry = $coreRegistry;
        $this->_resultPageFactory = $pageFactory;
        parent::__construct($context);
    }

    public function execute()
    {
        //Get ID and create model
        $entityId = $this->getRequest()->getParam('entity_id');
        $model = $this->_objectManager->create('Vendor\Module\Model\VoucherEntity');
        if($entityId) {
            $model->load($entityId);
            if(!$model->getId()) {
                $this->messageManager->addError(__('This entity no longer exists.'));
                /** \Magento\Backend\Model\View\Result\Redirect $resultRedirect */
                $resultRedirect = $this->resultRedirectFactory->create();
                return $resultRedirect->setPath('*/*/');
            }
        }

        /** @var \Magento\Framework\View\Result\Page $resultPage */
        $resultPage = $this->_resultPageFactory->create();
        //Register model to use later in blocks
        $this->_coreRegistry->register('voucher_entity', $model);
        return $resultPage;
    }
}

In your Block, you can get:$this->_coreRegistry->registry('voucher_entity');

You can create function in block example as below:

public function getEvents(){
        //get values of current page
        $page=($this->getRequest()->getParam('p'))? $this->getRequest()->getParam('p') : 1;
        //get values of current limit
        $pageSize=($this->getRequest()->getParam('limit'))? $this->getRequest()->getParam('limit') : 5;

        $collection = $this->_eventCollectionFactory->create();
        $collection->addFieldToFilter('is_active',1);
        $collection->setPageSize($pageSize);
        $collection->setCurPage($page);
        $collection->getSelect()->order('main_table.start_time asc');
        return $collection;     
    }

Using below code you can call this function in phtml file

$block->getEvents();

EDIT: How to get post data in block. you need to add below code in block

protected $request;
public function __construct(
    \Magento\Framework\App\Request\Http $request,
    ....
) {
   $this->request = $request;
}
public function getPostData()
{
  // you can use below code in any function       
  $postData =  $this->getRequest()->getParams();
}