When searching something on a phpBB forum, you are currently sending a POST request.
Why not search with a GET request with the query in the url (ex. http://example.com/phpbb/search.php?q=hello%20world) - just like any search engine.
This way you will be able to make it easier for people to change their searches (sometimes i just modify the url directly instead of resubmitting...)
And people will be able to search your site directly from their browsers...
-> http://<domain>/phpbb/search.php?q={query}




