Reverse the order of and in a wp_nav_menu

<ul>
    <a>
        <li></li>
    </a>
</ul>

Is not valid HTML. An <a> tag cannot be a child of a <ul> tag. So what you’re asking for isn’t possible. It’s not your actual problem either.

Your problem is a styling problem. If you want a larger touch target on the link, you need to add padding around the <a> tag, not the <li> tag.