Magento 2 - How to get the extension's configuration values in the phtml files?

You can create a function for getting configuration values in your custom module's helper.

<?php
namespace Vendor\Module\Helper;

class Data extends \Magento\Framework\App\Helper\AbstractHelper
{
    public function getConfig($config_path)
    {
        return $this->scopeConfig->getValue(
            $config_path,
            \Magento\Store\Model\ScopeInterface::SCOPE_STORE
        );
    }
}

Then you can get the configuration values to call this function in any phtml files.

$this->helper('Vendor\Module\Helper\Data')->getConfig('section/group/field');

Another way is as below

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$conf = $objectManager->get('Magento\Framework\App\Config\ScopeConfigInterface')->getValue('group/field/value');

<?php
namespace Vendor\Module\Helper;

class Data extends \Magento\Framework\App\Helper\AbstractHelper
{
    public function getConfig($config_path)
    {
        return $this->scopeConfig->getValue(
            $config_path,
            \Magento\Store\Model\ScopeInterface::SCOPE_STORE
        );
    }
}

$this->helper('Vendor\Module\Helper\Data')->getConfig('section/group/field');