How to get widget parameter in custom phtml or block?

use parameters in widget.xml

    <parameters>
        <parameter name="category_id" sort_order="10" visible="true" xsi:type="text">
            <label>124</label>
        </parameter>
    </parameters>

you can get this value in .phtml like

<?php echo $block->getData('category_id'); ?>

hope this will work for you.

I used ObjectManager but using the below code you can convert.

<?php
use \Magento\Framework\App\Bootstrap;
require __DIR__ . '/app/bootstrap.php';
$bootstrap     = Bootstrap::create(BP, $_SERVER);
$objectManager = $bootstrap->getObjectManager();
$instance      = \Magento\Framework\App\ObjectManager::getInstance();
$state         = $objectManager->get('\Magento\Framework\App\State');
$state->setAreaCode('frontend');

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$widgetCollection = $objectManager->create('Magento\Widget\Model\Widget\Instance');
//$data = $widgetCollection->load(instanceId);
$data = $widgetCollection->load('1');
echo "<pre/>";
print_r($data->getData());

Result