ΔE 22.6, loose: different enough that you should pick on purpose. Light Phthalo Green is much more saturated than Wrack White.
Can I use Light Phthalo Green instead of Wrack White?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Light Phthalo Green is much more saturated than Wrack White.
Can I use Wrack White instead of Light Phthalo Green?
The same difference applies the other way round: Wrack White is 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.