I want to build a web-application using the php, I have started with CodeIgniter and Smarty. The issue is I came to know opinion about this combination like "framework in 2015?, like a joke", there are so many framework and all the updated and and many more thing like socket and node.js and all which make me so confusing. I know many thing have there own need and work all the way, but I want to develop a site which will expecting 1-5 million hit monthly and I want it fast and efficient, using core php need to do more work which a good framework can do for you but still not sure what's the best approach to go from here.
Any top PHP framework like Laravel or Symfony can handle websites with so much traffic. If you want to create an API based on PHP and leave front-end to another app like Angular, you may also take a look a Lumen or Slim Framework.
I know it's a broad question but answer is simple, these frameworks give you the tools, as long as you follow modern principles and use caching they will be able to serve that many requests.