Phoenix Red vs Light Red

How close are they?

ΔE 16.9, loose: different enough that you should pick on purpose. Light Red is a little lighter, much more saturated than Phoenix Red.

Can I use Light Red instead of Phoenix Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Light Red is a little lighter, much more saturated than Phoenix Red.

Can I use Phoenix Red instead of Light Red?

The same difference applies the other way round: Phoenix Red is a little darker, much more muted.

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.