ΔE 16.3, loose: different enough that you should pick on purpose. Phthalo Green (Blue Shade) is noticeably lighter, more saturated than Vulkan Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Phthalo Green (Blue Shade) is noticeably lighter, more saturated than Vulkan Green.
The same difference applies the other way round: Vulkan Green is noticeably darker, 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 Vulkan Green on the colour wheel See Phthalo Green (Blue Shade) on the colour wheel
All matches: Vulkan Green equivalents · Phthalo Green (Blue Shade) equivalents