Electret condenser Binaural Recording

Hello I'm learning about electret condenser microphones and I saw this project on Make
http://makezine.com/projects/the-stealth-mic/#
They made a video about it:

I thought you need a power supply to work the microphones, why is there no mention of it in this build?
Would I just be able to plug it into my phone and have a recording, or would I need to amplify it first?

Thanks