If you are inside a phtml file, and you need to call an specific function inside another block. You can do the following:

• The block method  that you want to call is the following:
  
  1 2 3 4 5 6 7 8 9 10 11

  <?php namespace Vendor\MyModule\Block; use Magento\Framework\View\Element\Template;   class MyClass extends Block_Class {     public function myCustomMethod()     {         return '<b>Block Method i want to display</b>';     } }

• This is what you should do, in your phtml:
  
  1 2 3 4

  <?php $blockInstance= $block->getLayout()->createBlock('Vendor\MyModule\Block\MyClass'); echo $blockInstance->myCustomMethod(); ?>

  
   

Hope it helps.