before I begin please be ABSOLUTELY CERTAIN you are in 1.11.2 and not 1.12

For Phase One, you must kill the creeper that contains voltage, before it reaches 7, you must stand on a gold block, continue to do this again 2 more times but NEVER stand on the same gold block again, once there are no more gold blocks to stand on (3 times) you should be good to go, climb up to the top and step into the portal with bone blocks as it's frame, you should be in phase II now, if not the command block to teleport is behind the portal, use it's coordinates to get to phase II.

Phase I​​