ΔE 14.5, fair: the same colour family, but not a straight swap. Phthalo Cyanine Blue is noticeably darker, warmer than The Fang.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Phthalo Cyanine Blue is noticeably darker, warmer than The Fang.
The same difference applies the other way round: The Fang is noticeably lighter, 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 The Fang on the colour wheel See Phthalo Cyanine Blue on the colour wheel
All matches: The Fang equivalents · Phthalo Cyanine Blue equivalents