Can you tell me the meaning of these lyrics?

In Beyonce's, If I Were a Boy, she says:

If I were a boy

I would turn off my phone

Tell everyone it's broken

So they'd think that I was sleeping alone

I don't understand how a broken phone correlates to sleeping alone. Can someone explain this to me?

Also, Fall Out Boy's, My Songs Know What You Did in the Dark makes absolutely no sense to me. Does anyone know what the song is about?