ΔE 16.0, loose: different enough that you should pick on purpose. Imperial Purple is a little lighter, much more saturated, cooler than Phantom Violet.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Imperial Purple is a little lighter, much more saturated, cooler than Phantom Violet.
The same difference applies the other way round: Phantom Violet is a little darker, much 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 Phantom Violet on the colour wheel See Imperial Purple on the colour wheel
All matches: Phantom Violet equivalents · Imperial Purple equivalents