What is Phosphate Treatment 5.1.3.3 from spec 1.9.3?

A. Jason,
Your description is unclear. It sounds like you are looking at some document where the heading 1.9.3 refers to ASTM B633. It's unclear if the reference to 5.1.3.3 is for 5.1.3.3 in B633 or 5.1.3.3 in the document you are currently looking at. It's also possible that B633 once had a 5.1.3.3 that's since been removed, in which case referring to old/archival copies of B633 might help.

The best place to start asking would be the organization that published the document you are looking at. If you could identify for us the document you are looking at, maybe somebody here who is familiar with it could give better assistance.

A. From what I can tell, that's an error stemming in older revisions of MIL-STD-171.

Revision D has a section 5.1.3.3 covering supplementary treatments of zinc / cadmium before painting. The numbering of this section was changed to 5.1.4.3 in revision E, but the references in table II were not also updated.

Revision F, the most current, now lists finish 1.9.3 as "Electrodeposited zinc, ASTM B633, type IV, with supplementary phosphate treatment (see finish 5.1.1)".