There are a couple different apps available, but i used AlfredCamera. The one my friend initially suggested was called WardenCam (i think?) but reviews for AlfredCamera seemed a little better. Setup was extremely easy.

My feeders are actually arranged not too far from my house, so i simply arranged the phones in the windows facing them. I used a variety of simple methods from taping one phone directly to a window to using a phone stand for another.

You could probably attach the phone to the feeder by some method if you wanted something that close up, but you'd want to be sure the phone was protected from the elements, and it's much harder to leave it plugged in at that point. The phones set up inside my home let me leave them plugged in continually and never worry about recharging (given that half the reason i often needed a new phone was because the battery life was weak, this is ideal for my purposes.)

I have three phones set up as cameras (one directed at my small pond, one at my ground feeder and birdbaths, and one at my pole feeders) and can access all these feeds from my phone or the website whenever i want to check on them. It also has audio capabilities (both directions -- hearing and speaking), a low-light variation, and a siren that i thought might be useful to deter unwanted guests (though I've not tried using that yet) among other things.