Phoenix Flames vs Naples Yellow

How close are they?

ΔE 16.9, loose: different enough that you should pick on purpose. Naples Yellow is a little darker, more saturated, warmer than Phoenix Flames.

Can I use Naples Yellow instead of Phoenix Flames?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Naples Yellow is a little darker, more saturated, warmer than Phoenix Flames.

Can I use Phoenix Flames instead of Naples Yellow?

The same difference applies the other way round: Phoenix Flames is a little lighter, more muted, 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.