Invisible Tile Help

I'm trying to spawn a skull (I have the block spawned and stuff) but I need to spawn a tile so the skull isn't invisible. I tried using NBT tags but they aren't making much sense to me. Any help is appreciated.

How do you spawn it? I believe that would affect why.

PHP:

$level->setBlock(new Vector3($x,$y,$z), Block::get(144));
//$level is properly defined

That's why. You need to create a tile. Level::addTile and Tile::createTile();