Common
Phantasy Star (Classic Series) Hacking Guide
Document by GhaleonUnlimited that goes over general knowledge for hacking older Phantasy Star games.
Phantasy Star (Classic Series) Hacking Guide
Phantasy Star (Master System) Compression document
Document by g8z et al that goes over and provides C++ code for compression and decompression in Phantasy Star.
lory1990's disassemblies
Phantasy Star is one of the fortunate series to have ROM disassemblies.