There isn’t an is_mobile() function to my knowledge. WordPress uses a wp_is_mobile() which is probably what you’re looking for. So it should look like this:
<?php if ( wp_is_mobile() ) { wp_nav_menu( array('menu' => 'mobile' ) ); } else { wp_nav_menu( array('menu' => 'primary' ) ); }; ?>
EDIT
After reviewing your question further it seems like you have a plugin installed to browser sniff for you. It does look like it uses is_mobile() but since I am unfamiliar with the plugin I would suggest going vanilla with wp_is_mobile() instead of using a plugin, who knows what could be wrong with the plugin or if the plugin is compatible with your installation.
FINAL EDIT
It turns out according to OP that the menu names were not matching.
Related Posts:
- WordPress Menu Exchange On Tablet’s Orientation
- How to stop mobile theme inheriting desktop navigation menu?
- How to get a different mobile menu than desktop menu in the twentytwelve child theme
- Second nav is merged with the first in mobile
- Does WordPress create mobile menus automatically?
- Mobile menu works on local XAMPP, but not on GoDaddy [closed]
- WordPress Split Menu
- TwentyTwelve child theme mobile menu not working
- How to add a submenu toggle button inside all “li” elements that have a submenu?
- Convert WP Menu to a Drop Down for Mobile browser
- Add Button to Bottom of Mobile Menu
- burger on mobile
- Uber menu, manual integration, disable Mobile
- My Temptation theme is showing two of the same menu at the top. How do I remove the one that the theme comes with? Please help! [closed]
- Replace the slug of parent pages with # [closed]
- Menu Not Showing on Mobile
- Efficient wp mobile menu
- WordPress website – Mobile menu behavior help
- (Mobile) Hamburger menu disappeared from a page (only one)
- My menu doesn’t fit in the default screen in the mobile version
- Top bar menus not showing on mobile
- Mobile navigation javascript problem
- Replace the page url with a menu link?
- Mobile menu displays submenus on top of parent. Need it to display right below on an own line
- Menu doesn’t open on mobile
- Change menu for mobile
- Add href to tag in nav menu for mobile
- Disable Top Nav Bar on Mobile
- Mobile menu not working – jQuery error?
- menu mobile show up even i in desktop mode in Newspaper Theme
- Mobile Menu Not Working
- Theme: Twenty Thirteen Mobile Sliding Menu Doesn’t Bump Content Down
- Navigation menu, remove item from desktop
- Changing when mobile menu is displayed
- How can I only show one responsive menu on mobile devices?
- How to organize the header elements, so that it doesn’t come out differentin mobile view
- Moving active menu item onscreen for mobile
- issues with menu display on mobile & tablet – astra theme
- Display a portion/ branch of the menu tree using wp_nav_menu()
- Programmatically add a Navigation menu and menu items
- Any docs for wp_nav_menu’s “items_wrap” argument?
- Customizing Only a Specific Menu using the “wp_nav_menu_items” Hook?
- Changing the Order of Admin Menu Sections?
- How make top level menu item not have link, but have sub-menus that are linked?
- Add ‘has_children’ class to parent li when modifying Walker_Nav_Menu
- Get WP Navigation Menu from REST API V2
- How to Hard Code Custom menu items
- How to add a Custom Link to a Menu with a URL that is relative to the blog URL
- How do I remove UL on wp_nav_menu?
- Retrieving a list of menu items in an array
- WordPress default menu in database
- Adding an Arbitrary Link to the Admin Menu?
- Dynamically exclude menu items from wp_nav_menu
- Add “Logout” link to navigation menu
- Error: Declaration of MyClass::start_lvl() should be compatible with that of Walker_Nav_Menu::start_lvl()
- Split up wp_nav_menu with custom walker
- Removing container from wp_nav_menu not working
- Custom Nav walker display current menu item children, or siblings on no children
- wp_nav_menu: show menu only if one exists, otherwise show nothing
- Is there an easy way to replace a custom menu link with a page or post?
- Convert output of nav_menu items into a tree-like multidimensional array
- Get page IDs from nav items
- Add a custom walker to a menu created in a widget
- Using a menu walker add a custom item at the end of the menu’s items
- Add settings to menu items in the Customizer
- wp_get_nav_menu_items() not working with slug
- How to get current-menu-item title as variable?
- Error “Trying to get property of non-object” with Custom Walker for wp_nav_menu
- Add Class to Specific Link in Custom Menu
- Remove a menu item in menu
- Generate a Menu that Displays Child Pages using wp_list_pages() with the New Menu Functionality in WordPress 3.0?
- How do I get the name of a menu in WordPress?
- How to Add to Each Menu Link with link text to data-attr?
- How to manually specify the current active page with wp_nav_menu()
- How to count nav menu items?
- How Does The Walker Class Work?
- Add Javascript to WordPress Menu
- Add custom menu item using wp_nav_menu_items filter
- Filter wp_nav_menu()
- How to modify navigation menu of the “My Account” page in WooCommerce
- remove “edit your profile” from admin menu bar
- WordPress Settings API, Implementing Tabs On Custom Menu Page
- Adding line breaks to nav menu items
- Adding category ID or slug to WP Nav Menu
- add custom class to wp_nav_menu using filter hook nav_menu_css_class
- Custom ID for certain menu item?
- Does Extending Multiple Nav_Menu_Walkers Allow Nested Menus?
- Check if page is in a certain menu
- how to create a menu with all sub categories?
- Making breadcrumb with wp_nav_menu
- Does WP REST API have a built in route for calling menu?
- How to avoid wp_nav_menu() ID conflict?
- Add data-icon input to WordPress custom menu links
- Registering menu with ‘Automatically add new top-level pages to this menu’ selected
- Why do Custom Nav Menus generate so many classes on list items? Can I manage this somehow?
- wp_nav_menu remove class and id from li
- Custom search filter causes menu and query_posts problems
- Unregister Nav Menu from Child-Theme
- How does a minimal menu walker look like?
- Add separator to admin submenu