ΔE 23.8, loose: different enough that you should pick on purpose. Aquamarine is noticeably lighter, more saturated, cooler than Light Turquois (Phthalo).
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Aquamarine is noticeably lighter, more saturated, cooler than Light Turquois (Phthalo).
The same difference applies the other way round: Light Turquois (Phthalo) is noticeably darker, more muted, warmer.
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 Light Turquois (Phthalo) on the colour wheel See Aquamarine on the colour wheel
All matches: Light Turquois (Phthalo) equivalents · Aquamarine equivalents