magento 2.3 call customer group Name

Try this code

 protected $_session;
 protected $_customerGroupCollection;

 public function __construct(
        ................................................
        MagentoCustomerModelSession $session,
        MagentoCustomerModelGroup $customerGroupCollection,
        ................................................
    ) {
        ................................................
        $this->_session = $session;
        $this->_customerGroupCollection = $customerGroupCollection;
        ................................................
    }
    public function getGroup()
    {
        $currentGroupId = $this->_session->getCustomer()->getGroupId(); //Get customer group Id 
        $collection = $this->_customerGroupCollection->load($currentGroupId); 
        echo $collection->getCustomerGroupCode();//Get group name
    }

Call this method in phtml

$block->getGroup();

I Hope This Helps You.