Call php function from javascript file Magento 2

I add an custom checkbox html to Magento checkout page

First, I add the Hello component to the checkout XML. This use Hello_Widget/checkout/shipping/widget as HTML template and Hello_Widget/js/view/checkout/shipping/widget as javascript file.

// checkout_index_index.xml

                            <item name="steps" xsi:type="array">
                                <item name="children" xsi:type="array">
                                    <!-- Modifying an existing step-->
                                    <item name="shipping-step" xsi:type="array">
                                        <item name="children" xsi:type="array">
                                            <item name="shippingAddress" xsi:type="array">
                                                <item name="children" xsi:type="array">
                                                    <item name="shippingAdditional" xsi:type="array">
                                                        <item name="component" xsi:type="string">uiComponent</item>
                                                        <item name="displayArea" xsi:type="string">shippingAdditional</item>
                                                        <item name="children" xsi:type="array">
                                                 <!-- LOOK HERE ONLY-->
                                           <item name="hello_input" xsi:type="array">
                                                                <item name="component" xsi:type="string">Hello_Widget/js/view/checkout/shipping/widget</item>
                                                                <item name="config" xsi:type="array">
                                                                    <item name="template" xsi:type="string">Hello_Widget/checkout/shipping/widget</item>
                                                                    <item name="title" xsi:type="string" translate="true">HelloInput</item>
                                                                </item>
                                                            </item>
                                                        </item>
                                                    </item>
                                                </item>
                                            </item>
                                        </item>
                                    </item>

                                </item>
                            </item>
                        </item>
                    </item>
                </item>
            </argument>
        </arguments>
    </referenceBlock>
</body>

// widget.html: This is the HTML with simple checkout input

// widget.js: This is javascript file

define([
    'Magento_Checkout/js/view/summary/abstract-total',
    'Magento_Checkout/js/model/totals'
], function (Component, totals) {
    "use strict";

    return Component.extend({

        /** Some code here **/

        /**
         * Is display reward points totals
         *
         * @return {boolean}
         */
        isDisplayed: function() {
            return true
        },

        /**
         * Click handler
         */
        onClick: function () {
           console.log('click from HELLO') // WATCH HERE
           // HERE want to call the PHP function to add isChecked: true to the Magento Session
        },
    });
});

Note that I extend the abstract-total for some reasons and you don’t need to care about it now. When I click the checkbox, I can use jQuery to listen to the event (see onClick function).Here I want to call the PHP function to add isChecked: true to the Magento Session. The onClick function in javascript file should trigger the handleCheckbox in PHP file and pass the checkbox value

// Some PHP file (I think I could be some block)

class CustomBlock {
  constructor(Session) {...}

  handleCheckbox(value) {session.setValue(array([isChecked => value]))} // sth like this
}

Could you guys show me how to do it? Thanks