ΔE 15.6, loose: different enough that you should pick on purpose. Sun Yellow is a little lighter, more saturated, cooler than Phalanx Yellow.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Sun Yellow is a little lighter, more saturated, cooler than Phalanx Yellow.
The same difference applies the other way round: Phalanx Yellow is a little darker, more muted, warmer.
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 Phalanx Yellow on the colour wheel See Sun Yellow on the colour wheel
All matches: Phalanx Yellow equivalents · Sun Yellow equivalents