ΔE 18.1, loose: different enough that you should pick on purpose. Phthalo Green (Blue Shade) is noticeably darker, much more saturated than Potion Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Phthalo Green (Blue Shade) is noticeably darker, much more saturated than Potion Green.
The same difference applies the other way round: Potion Green is noticeably lighter, 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.
See Potion Green on the colour wheel See Phthalo Green (Blue Shade) on the colour wheel
All matches: Potion Green equivalents · Phthalo Green (Blue Shade) equivalents