For women's groups such as Alpha Phi, Phi is pronounced "Fee" as it is the feminine and it comes at the end.

However, other women's groups such as Delta Phi Epsilon and Phi Mu, it is pronounced "Fie" (I think...I could be wrong)

Similarly, the women's sorority Alpha Xi Delta, the Xi is pronounced "Zee", not "Zigh" (like sigh, but with a z sound).