ΔE 17.0, loose: different enough that you should pick on purpose. Sky Blue is noticeably lighter, warmer than Phthalo Turquoise Light.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Sky Blue is noticeably lighter, warmer than Phthalo Turquoise Light.
The same difference applies the other way round: Phthalo Turquoise Light is noticeably darker, 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 Turquoise Light on the colour wheel See Sky Blue on the colour wheel
All matches: Phthalo Turquoise Light equivalents · Sky Blue equivalents