When you open your computer:
Right click on the iPhoto icon in the Dock. Is Open at Log In Selected?
Check your System Preferences -> Accounts -> Log In Items
Is there a camera or anything that your Mac might think is a camera (flash drive, USB Hard Disk formatted to a FAT format, phone) attached to your Mac. If so, disconnect it. If you don't want to disconnect it, set iPhoto to "Do Nothing" when a camera is attached. You do this in the iPhoto Preferences.
When you connect your Phone:
Iphoto -> Preferences -> General / Connecting Camera opens... And select No Application