As with most names of cities, the of is optional in the phrase “the city (of) Nephihah”. Here we have two examples where the of was lacking in the earliest text. In both cases, the of was added to the LDS text in the 1879 edition. And the LDS text has continued with the of in both these cases. The of was also added to the RLDS text in the 1874 edition but only in the first case. In that instance, the 1908 RLDS edition removed the extra of from the RLDS text, probably by reference to 𝓟.
There are eight other instances in the text of “the city of Nephihah” but none of “the city Nephihah”. In one of these cases, Oliver Cowdery initially omitted the of in 𝓟. Virtually immediately he supplied the of by supralinear insertion (there is no change in the level of ink flow):
𝓞 is not extant here but presumably had the of. The critical text will, in each case, follow the earliest textual sources, thus restoring the two original occurrences of “the city Nephihah” here in Alma 62:18.
Summary: Restore the two original occurrences of “the city Nephihah” in Alma 62:18 (in accord with 𝓟, the earliest textual source for these two occurrences); maintain the of in “the city of Nephihah” for all other instances in the text, including Alma 62:30.