I have used http://testuri.org/sniffer to check the content but found out that PHPBB3 serves a totally different content for example: http://codingforspeed.com/forum/viewtopic.php?f=4&t=59
the google bots are not able to read them. So, how to make phpbb indexed by google? currently if I google site:http://codingforspeed.com/forum/ it only returns 1 index page.
Figured out the solution, which is to manually add googlebot to phpbb
https://helloacm.com/how-to-fix-phpbb3-1-5-not-indexed-by-googlebots/