Indexing for Layer, Effect, and Mask elements in After Effects starts from 1. For example, the first layer in the Timeline panel is layer(1).

Generally, it is best to use the name of a layer, effect, or a mask instead of a number to avoid confusion and errors if the layer, effect, or mask is moved, or if the arguments are changed during product updates and upgrades. When you use a name, always enclose it in straight quotes. For example, the first expression below is easier to understand than the second expression, and the first expression will continue to work even if you change the order of effects:

  effect("Colorama").param("Get Phase From")  
  effect(1).param(2)