ΔE 18.8, loose: different enough that you should pick on purpose. Phalanx Yellow is a little darker, warmer than Fluorescent Yellow. They are different kinds of paint: AK Interactive Fluorescent Yellow is a fluorescent or effect paint and Citadel Phalanx Yellow is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Phalanx Yellow is a little darker, warmer than Fluorescent Yellow. They are different kinds of paint.
The same difference applies the other way round: Fluorescent Yellow is a little lighter, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Fluorescent Yellow on the colour wheel See Phalanx Yellow on the colour wheel
All matches: Fluorescent Yellow equivalents · Phalanx Yellow equivalents