ΔE 17.4, loose: different enough that you should pick on purpose. Light Phthalo Blue is noticeably lighter, more saturated, warmer than Briar Queen Chill. They are different kinds of paint: Citadel Briar Queen Chill is a one-coat contrast-style paint and Golden Light Phthalo Blue is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Light Phthalo Blue is noticeably lighter, more saturated, warmer than Briar Queen Chill. They are different kinds of paint.
The same difference applies the other way round: Briar Queen Chill 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 Briar Queen Chill on the colour wheel See Light Phthalo Blue on the colour wheel
All matches: Briar Queen Chill equivalents · Light Phthalo Blue equivalents