Poppy Red vs Phoenix Orange

How close are they?

ΔE 15.1, loose: different enough that you should pick on purpose. Phoenix Orange is noticeably darker, warmer than Poppy Red.

Can I use Phoenix Orange instead of Poppy Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Phoenix Orange is noticeably darker, warmer than Poppy Red.

Can I use Poppy Red instead of Phoenix Orange?

The same difference applies the other way round: Poppy Red is noticeably lighter, cooler.

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.