You can try this module
<!-- app/code/Sanne/Js/etc/module.xml -->
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
<module name="Sanne_Js" setup_version="1.0.0">
<sequence> <module name="Magento_Checkout" /></sequence>
</module>
</config>
// app/code/Sanne/Js/registration.php
<?php
\Magento\Framework\Component\ComponentRegistrar::register(
\Magento\Framework\Component\ComponentRegistrar::MODULE,
'Sanne_Js',
__DIR__
);
<!-- app/code/Sanne/Js/view/frontend/layout/checkout_index_index.xml -->
<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="checkout" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceContainer name="content">
<block class="Magento\Framework\View\Element\Template" name="phonejs" template="Sanne_Js::js.phtml" />
</referenceContainer>
</body>
</page>
<!-- app/code/Sanne/Js/view/frontend/templates/js.phtml -->
<?php ?>
<script type="text/x-magento-init">
{
"*": {
"Elgentos_AddTelephoneInputType/js/phonevalidation":
{
"phoneinput":"input[name=telephone]"
}
}
}
</script>
// app/code/Sanne/Js/view/frontend/web/js/phonevalidation.js
define([
"jquery",
"jquery/ui"
], function($) {
"use strict";
//creating jquery widget checking phone numbers to remove character, allowed only numbers
$.widget('phonevalidation.js', {
_create: function() {
var widget = this;
var templateoptions = widget.options;
$('body').on('input', templateoptions.phoneinput, function() {
var number = $(this).val().replace(/[^\d]/g, '');
$(this).val(number)
});
}
});
return $.phonevalidation.js;
});
// app/code/Sanne/Js/view/frontend/web/requirejs-config.js
var config = {
map: {
'*': {
phonevalidationjs: 'Sanne_Js/js/phonevalidation'
}
}
};
<!-- app/code/Sanne/Js/view/frontend/layout/customer_address_form.xml -->
<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceContainer name="content">
<block class="Magento\Framework\View\Element\Template" name="phonejs" template="Sanne_Js::js.phtml" />
</referenceContainer>
</body>
</page>