From the left, the first telephone port is for line that comes from line owner, that is Telekom. So you plug the line that comes from the building. (I assume you are high rise like Condo or shop house).

The next 4 yellow ports is the ones where you connect a cable to the Maxis router (black on right). You can use any of the yellow ports. So you got it correct here.

The blue are output for telephone. This only works for Telekom broadband only. If you are on Maxis, you need to plug your house telephone to the Maxis (black) router phone port which is green. What you can do now is, make sure the correct building telephone line that comes from the wall is plugged in to the left most telephone port on the TM BTU @ modem and not a house telephone unit.

The black Maxis router seems correctly plugged. The cable that comes from the BTU@Modem is plugged correctly to WAN (red port), so you got it right here as well.. Except the house telephone line that needs to be connected to the green port for the house telephone to work. (NOT THE BUILDING WALL TELEPHONE LINE)

Thanks for the help. Just solved it by calling maxis. But you can't simply plug into the lan ports :/

Apparently, LAN 1 on BTU BELONGS TO UNIFI. So you will have to plug into LAN 2 for it to work.

Thread will stay open for future reference for noobs like me 

TL;DR

WAN from router connect to LAN 2 on BTU