Looks like I misunderstood some concepts of working with Composer in PhpStorm. Here's the case.
I work with legacy application and need to use Twig and PHPWord packages. When I install it ($ composer require <package/name> ) through CLI PhpStorm adds new directories in vendor/ to Settings - Directories - Excluded Folders. And I can not use auto-import and/or auto-complete for those newly installed packages until I manually remove (eg. vendor/phpoffice/phpword) from Excluded Folders. Is it normal behaviour or I need properly setup PhpStorm to not auto-exclude 'main' Composer packages folder?