ΔE 19.0, loose: different enough that you should pick on purpose. Phthalo Green is noticeably darker, more muted, warmer than Turquoise Siren.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Phthalo Green is noticeably darker, more muted, warmer than Turquoise Siren.
The same difference applies the other way round: Turquoise Siren is noticeably lighter, 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 Turquoise Siren on the colour wheel See Phthalo Green on the colour wheel
All matches: Turquoise Siren equivalents · Phthalo Green equivalents