Shashank,
I'm going to spew some instructions here, but they're un-tested.. so you may run into issues. If you implement them in PHPBB though, it should be enough to let us see what's wrong (if something is), and give you a few more instructions...
Most of this is copying some code from you Joomla HTML output and hard-coding it into your PHPBB template file. This will basically recreate a lot of what JFBConnect is doing dynamically, and just make it static on your page.
1) Visit your home page, and open up the source HTML
2) Search for jfbconnect.js, you should see a line like below in the <head> section. Copy this to your PHPBB template:
<script type="text/javascript" src="/components/com_jfbconnect/includes/jfbconnect.js"></script>
3) Search for jfbcLogoutFacebook. This will be in a big <script type="text/javascript" block. Copy this whole block to your <head> section of PHPBB
4) Finally, search for "fb:login-button", you should see something like below. Copy this line wherever you want the Login With Facebook button to appear:
<fb :login-button v="2" onlogin="javascript:jfbc.login.login_button_click();">Login With Facebook</ fb:login-button>
Hopefully that makes sense, and will work out well for you. Again, once you get that, I'm sure there will be some things to iron out, but if we can get the Login With Facebook button to appear, we'll be in a good spot. I don't think we'll ever get the [JFBCLike] tag to work, but it's pretty easy to add manually, just so you know.