Phalanx Yellow vs Yellow FS33531

How close are they?

ΔE 17.7, loose: different enough that you should pick on purpose. Yellow FS33531 is a little darker, much more muted than Phalanx Yellow.

Can I use Yellow FS33531 instead of Phalanx Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Yellow FS33531 is a little darker, much more muted than Phalanx Yellow.

Can I use Phalanx Yellow instead of Yellow FS33531?

The same difference applies the other way round: Phalanx Yellow is a little lighter, much more saturated.

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.