Phantom Blocks were first seen in the video released in December 2011, these blocks are the key to the construction system of the game. A Phantom Block appears where a new block is to be placed by a Bricktron allowing the player to set future progress of construction and to keep a visual representation of what is to be built.
The Phantom Block takes the shape of whatever block is going to be placed, such as a stair block or simply a regular stone block (as seen to the right). Once a Phantom Block is placed, builder Bricktrons will proceed to use blocks from the Stockpile to fill in the Phantom area until the stockpile is depleted. You can also delete an unwanted block(s) by holding Control and selecting the block(s)
If a Phantom Block is inaccessible, the Bricktrons will ignore it until they can access it. For this reason, it is likely to cause a laggy game if the player places a lot of inaccessible Phantom Blocks and has a lot of builder Bricktrons who are doing nothing else, however this is merely hypothetical.