The voice, implied to be Asriel Flowey mimicking his voicecalls the protagonist by the name given to the Fallen Human at the beginning of the game, and tells them that 'everything has fallen into place' and that they will 'see you soon. Alphys explains that a robot she created, Mettaton, wants to kill the protagonist. Not interested, followed on accident T After delivering the letter to Alphys, she mistakes the letter as being from the protagonist themself and goes on a date with them. Flirt, that's always the answer.
True Pacifist Route
Alphys thanks the protagonist for their support and declares to the Amalgamates that they will return home.
Undertale: Alphys date flowchart
Surprised at the protagonist's high determination, Asriel reveals that he was only using a fraction of his real power. Believing they might have heard this a hundred times already, he says his goodbyes to the player, calling them by the name given to the fallen human at the beginning of the game. She explains that she has watched the protagonist throughout their journey using hidden cameras  and adds that she wants to help guide the protagonist through Hotland.