An example of how to create a custom taxonomy.

register-custom-taxonomy.php

<?php

class Register_Custom_Taxonomy
{
    public function __construct()
    {
        add_action('init', array( $this, 'Register_Operating_System_Taxonomy' ), 0);
        add_action('init', array( $this, 'Register_MakeModel_Taxonomy' ), 0);
    }

    public function Register_Operating_System_Taxonomy()
    {
        $labels = array(
            'name' => _x('Operating Systems', 'Taxonomy General Name', 'text_domain'),
            'singular_name' => _x('Operating System', 'Taxonomy Singular Name', 'text_domain'),
            'menu_name' => __('Operating System', 'text_domain'),
            'all_items' => __('All Items', 'text_domain'),
            'parent_item' => __('Parent Item', 'text_domain'),
            'parent_item_colon' => __('Parent Item:', 'text_domain'),
            'new_item_name' => __('New Item Name', 'text_domain'),
            'add_new_item' => __('Add New Item', 'text_domain'),
            'edit_item' => __('Edit Item', 'text_domain'),
            'update_item' => __('Update Item', 'text_domain'),
            'view_item' => __('View Item', 'text_domain'),
            'separate_items_with_commas' => __('Separate items with commas', 'text_domain'),
            'add_or_remove_items' => __('Add or remove items', 'text_domain'),
            'choose_from_most_used' => __('Choose from the most used', 'text_domain'),
            'popular_items' => __('Popular Items', 'text_domain'),
            'search_items' => __('Search Items', 'text_domain'),
            'not_found' => __('Not Found', 'text_domain'),
            'no_terms' => __('No items', 'text_domain'),
            'items_list' => __('Items list', 'text_domain'),
            'items_list_navigation' => __('Items list navigation', 'text_domain'),
        );

        $args = array(
            'labels' => $labels,
            'hierarchical' => false,
            'public' => true,
            'show_ui' => true,
            'show_admin_column' => true,
            'show_in_nav_menus' => true,
            'show_tagcloud' => true,
        );

        register_taxonomy('os', array('phone'), $args);
    }

    public function Register_MakeModel_Taxonomy()
    {
        $labels = array(
            'name' => _x('Make and Models', 'Taxonomy General Name', 'text_domain'),
            'singular_name' => _x('Make and Model', 'Taxonomy Singular Name', 'text_domain'),
            'menu_name' => __('Make and Models', 'text_domain'),
            'all_items' => __('All Items', 'text_domain'),
            'parent_item' => __('Parent Item', 'text_domain'),
            'parent_item_colon' => __('Parent Item:', 'text_domain'),
            'new_item_name' => __('New Item Name', 'text_domain'),
            'add_new_item' => __('Add New Item', 'text_domain'),
            'edit_item' => __('Edit Item', 'text_domain'),
            'update_item' => __('Update Item', 'text_domain'),
            'view_item' => __('View Item', 'text_domain'),
            'separate_items_with_commas' => __('Separate items with commas', 'text_domain'),
            'add_or_remove_items' => __('Add or remove items', 'text_domain'),
            'choose_from_most_used' => __('Choose from the most used', 'text_domain'),
            'popular_items' => __('Popular Items', 'text_domain'),
            'search_items' => __('Search Items', 'text_domain'),
            'not_found' => __('Not Found', 'text_domain'),
            'no_terms' => __('No items', 'text_domain'),
            'items_list' => __('Items list', 'text_domain'),
            'items_list_navigation' => __('Items list navigation', 'text_domain'),
        );

        $args = array(
            'labels' => $labels,
            'hierarchical' => true,
            'public' => true,
            'show_ui' => true,
            'show_admin_column' => true,
            'show_in_nav_menus' => true,
            'show_tagcloud' => true,
        );

        register_taxonomy('makemodel', array('phone'), $args);
    }
}

return new Register_Custom_Taxonomy();