How to get phrase tables from word alignments?
This isn't my area of specialty and I'm not familiar with Moses, but I found this after some searching.  

I think you are looking for GIZA++.  You'll see GIZA++ listed in the "Training" section (left menu) on the Moses home page, as the second step. GIZA++ is briefly described in tutorial fashion here. Here are a few tutorial PowerPoint slides: http://www.tc.umn.edu/~bthomson/wordalignment/GIZA.ppt