ΔE 24.6, loose: different enough that you should pick on purpose. Alien Purple is noticeably lighter, much more muted, warmer than Phthalo Blue (Green Shade).
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Alien Purple is noticeably lighter, much more muted, warmer than Phthalo Blue (Green Shade).
The same difference applies the other way round: Phthalo Blue (Green Shade) is noticeably darker, much more saturated, 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.
See Phthalo Blue (Green Shade) on the colour wheel See Alien Purple on the colour wheel
All matches: Phthalo Blue (Green Shade) equivalents · Alien Purple equivalents