There is no way to install Flash player on an iOS device. The only workaround is to install one of the browser apps that takes Flash content and converts it via a remote server to a form that will play on the iOS device. Several examples are Puffin Browser, Photon, and Skyfire. Using apps like these to view Flash content will result in a reduction in picture quality but are the only option for the iPhone.
This article explains why Apple doesn't allow Flash on it's iOS devices. Thoughts on Flash