The manganese phosphate coating is going to be a much harder and better wear resistant coating to the zinc coating.
The Wiki on
manganese phosphate is very knowledgeable. You may get a better understanding of the processes involved here if you haven't read up on the process. This
site has a good short write up as well.
I used to do thermal spay zinc coating on bridges so I understand the process quite well, but would have a hard time explaining it. Corrosion coating processes like this are quite fascinating how they work. I was working with a guy few years back developing zinc and nano powdered plastic coatings trying to prolong hull coating erosion from sand/salt erosion, barnacle growth, and one that would prevent mud from building up on canal lock doors, that was 10 times sicker than ptfe teflon.
Not trying to hijack the thread. Just interested in the discussion.