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