Clone the “proceed to cart” button and place it above checkout on the cart page, but only appear display size is 320px

Just call woocommerce proceed-to-checkout-button template in woocommerce_before_cart action hook as follows-

add_action('woocommerce_before_cart', 'add_wc_button_proceed_to_checkout');
function add_wc_button_proceed_to_checkout(){
    echo '<div class="wc-proceed-to-checkout">';
    wc_get_template( 'cart/proceed-to-checkout-button.php' );
    echo '</div>';
}