Integrating mobile device detection into your PHPBB forum is pretty straightforward.

  1. Download a phpbb mobile style (eg art_mobile) and upload to styles/ dir, no need to install it.
  2. Copy ‘mobile.php/ from styles/art_mobile/contrib/ to /includes/
  3. Edit includes/session.php as below.

Find this line:

// Call phpbb_user_session_handler() in case external application want to "bend" some variables or replace classes...
// After calling it we continue script execution...

Enter above it (above the comments):

// Mod: phpBB Mobile start
include_once($phpbb_root_path . 'includes/mobile.' . $phpEx);
phpbb_mobile::setup('art_mobile'); // Change first parameter to correct directory name of mobile style
// Mod: phpBB Mobile end

Save the file and that’s it. Now there will be a button to swap between the mobile and full site. Re-directions are done automatically.

Thanks to Artodia for this information.