Sean Breeden

In Magento 2, it's possible to call any block into any phtml with two lines of code. Ideally, dependency injection should be used but I'll demonstrate both methods. I will use FirstModule and SecondModule to distinguish between the two modules.

The correct way

In the Block construct for your FirstModule phtml:

namespace Vendor\FirstModule\Block;

class Custom extends Template
{

private $custom;

public function __construct(
 ...
 \Vendor\SecondModule\Block\Custom $custom
 ...
) {
 ...
 $this->custom = $custom;
 ...
}

public function getCustomMethod()
{
 // This references the "SecondModule" Custom class
 $custom = $this->custom;
 // Returns the getCustomMethod() from the "SecondModule"
 return $custom->getCustomMethod();
}

In the FirstModule phtml where the SecondModule "getCustomMethod" output will be displayed:

<?= $block->getCustomMethod(); ?>

The not-as-correct way that also works (no injection)

In the FirstModule phtml where the custom SecondModule output will be displayed:

<?php
 $customBlock = $block->getLayout()->createBlock('Vendor\SecondModule\Block\Custom');
 echo $customBlock->getCustomMethod();
?>