ΔE 16.7, loose: different enough that you should pick on purpose. Light Phthalo Blue is noticeably lighter, more saturated than Ice Storm.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Light Phthalo Blue is noticeably lighter, more saturated than Ice Storm.
The same difference applies the other way round: Ice Storm is noticeably darker, more muted.
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 Ice Storm on the colour wheel See Light Phthalo Blue on the colour wheel
All matches: Ice Storm equivalents · Light Phthalo Blue equivalents