How to avoid iOS devices being first selection when launching iPhoto
Iphoto>Preferences>General>Connecting A Camera>Opens No Application.

or 

you can do it through the Image Capture application. There is a pane in the lower left where you can change the preferences when the iPhone is connected.

So
1. connect the phone
2. open Image Capture
3. change the settings for the iPhone which is treated as a camera.