ΔE 23.9, loose: different enough that you should pick on purpose. Light Phthalo Blue is noticeably lighter, more muted than Aegis Aqua.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Light Phthalo Blue is noticeably lighter, more muted than Aegis Aqua.
The same difference applies the other way round: Aegis Aqua is noticeably darker, 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 Light Phthalo Blue on the colour wheel
All matches: Aegis Aqua equivalents · Light Phthalo Blue equivalents