The Phelps reloaders are for the most part pretty good copies of Stars, but unlike Stars which changed very little over their production history, it's hard to find two Phelps that are exactly alike. Most of the early Phelps that were actually produced by John Phelps are pretty good. Not as exact or consistent as a Star, but still a decent reloader. After Phelps suffered bankruptcy and stopped producing reloaders, the assets were bought by Dan Fausto. Fausto continued to put together machines from parts, and may have had some additional parts made, but in my opinion, the overall quality went down hill. I have seen some really bad Phelps reloaders.....but also some nice ones.
So echoing Dave's comments, many parts are interchangeable, but not all, and the interchangeability might depend on the particular Phelps reloader you have.
Bruce