vBulletin 5 uses responsive design by default as part of its Mobile Application Suite. You may be able to find 3rd party responsive design options for prior versions of vBulletin.
Find more information about the Mobile Application Suite on vBulletin’s website.
Is my vBulletin site mobile-friendly now?
We hope your site is now mobile-friendly and ready to be served to your mobile audience. We invite you to use the Mobile-Friendly Test tool now.
If the test results are not satisfactory or you have further questions, we welcome you on our international webmaster forums for additional guidance and support.
It’s also a good idea to check themes with our PageSpeed Insights tool. A high score with this tool is a good sign that your chosen theme will work well with mobile devices.