In Magento, you can change the display order of fields in the checkout page by using the sortOrder property see below for example.
The field to change is checkout_index_index.xml
<?xml version="1.0" encoding="UTF-8"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="checkout" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceBlock name="checkout.root">
<arguments>
<argument name="jsLayout" xsi:type="array">
<item name="components" xsi:type="array">
<item name="checkout" xsi:type="array">
<item name="children" xsi:type="array">
<item name="steps" xsi:type="array">
<item name="children" xsi:type="array">
<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="shipping-address-fieldset" xsi:type="array">
<item name="children" xsi:type="array">
<item name="postcode" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="string">5</item>
</item>
</item>
<item name="region_id" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="string">10</item>
</item>
</item>
<item name="city" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="string">15</item>
</item>
</item>
<item name="company" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="string">20</item>
</item>
<item name="validation" xsi:type="array">
<item name="min_text_length" xsi:type="number">0</item>
</item>
</item>
<item name="fax" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="string">25</item>
</item>
<item name="validation" xsi:type="array">
<item name="min_text_length" xsi:type="number">0</item>
</item>
</item>
<item name="country_id" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="string">100</item>
</item>
</item>
<item name="telephone" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="string">110</item>
<item name="tooltip" xsi:type="array">
<item name="description" xsi:type="string" translate="true">For delivery questions.</item>
</item>
</item>
</item>
<item name="vat_id" xsi:type="array">
<item name="config" xsi:type="array">
<item name="sortOrder" xsi:type="string">115</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</item>
</argument>
</arguments>
</referenceBlock>
</body>
</page>
Please change the corresponding numbers for the fields where you want them to appear at the top or bottom