Hot Pink vs Phantom Violet

How close are they?

ΔE 33.9, loose: different enough that you should pick on purpose. Phantom Violet is noticeably darker, much more muted, cooler than Hot Pink.

Can I use Phantom Violet instead of Hot Pink?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 34). Phantom Violet is noticeably darker, much more muted, cooler than Hot Pink.

Can I use Hot Pink instead of Phantom Violet?

The same difference applies the other way round: Hot Pink 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.