Phoenician Purple vs Plum

How close are they?

ΔE 15.6, loose: different enough that you should pick on purpose. Plum is noticeably lighter, more saturated, cooler than Phoenician Purple.

Can I use Plum instead of Phoenician Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Plum is noticeably lighter, more saturated, cooler than Phoenician Purple.

Can I use Phoenician Purple instead of Plum?

The same difference applies the other way round: Phoenician Purple is noticeably 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.