Alp possibly has some hard wear patches to give a bit more protection to jacket in a fall…phantom possibly heavier material so much warmer.
I have phantom, or might be phantom 2 and it is proper warm…I also have something else that is similar to the alp and it is much lighter but has a bit more abrasion protection on arms and shoulders. Both are very wind proof but the non phantom one doesn’t have removable arms and is incredibly thin…like condom thin!
I’m sure the alp-x range was designed for the more abrasive world of mtbing I.e. scuffing trees, rocks and landing on very uneven surfaces.
I think.