ΔE 22.2, loose: different enough that you should pick on purpose. Light Turquois (Phthalo) is noticeably lighter, more saturated, warmer than Deep Azure.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Light Turquois (Phthalo) is noticeably lighter, more saturated, warmer than Deep Azure.
The same difference applies the other way round: Deep Azure is noticeably darker, more muted, 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 Deep Azure on the colour wheel See Light Turquois (Phthalo) on the colour wheel
All matches: Deep Azure equivalents · Light Turquois (Phthalo) equivalents