The Phone is what Dave refers to the cell phone in his possession as. It is a major source of video capturing in Let's 0 and likely the sole video capturing device in the series.
Communications known to have come in to Dave through The Phone include:
In 11, he gets a voice mail telling him about a dental appointment.
27 is another voice mail, where Dave is told by the caller that they know he's not dead.
The description for 37 states that Dave got this video as a text message attachment which automatically downloaded.