Impish Rouge vs Phantom Violet

How close are they?

ΔE 32.1, loose: different enough that you should pick on purpose. Phantom Violet is noticeably darker, much more muted, cooler than Impish Rouge.

Can I use Phantom Violet instead of Impish Rouge?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Phantom Violet is noticeably darker, much more muted, cooler than Impish Rouge.

Can I use Impish Rouge instead of Phantom Violet?

The same difference applies the other way round: Impish Rouge is noticeably lighter, much more saturated, 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.