In Episode 9 of Steins;Gate, why did Feris's message affect the past?
The mistake you're making is that the phone attached to the microwave is irrelevant—any phone is okay.

The phone that matters is the phone that the microwave phone sends the message to.

The message is sent to Faris's father, Yukitaka Akiha.

The reason could be classed as spoilers, so make sure you watch the show first.


   Yukitaka died in a plane crash several years before the events of Steins;Gate. He was the only victim of the crash. However, his daughter later uses a D-Mail to save his life, by making him believe she was kidnapped and forcing him to take the bullet train instead.