ΔE 21.1, loose: different enough that you should pick on purpose. Mummy White is a little darker, much more muted, cooler than Phoenix Feather.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Mummy White is a little darker, much more muted, cooler than Phoenix Feather.
The same difference applies the other way round: Phoenix Feather is a little lighter, much more saturated, warmer.
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 Phoenix Feather on the colour wheel See Mummy White on the colour wheel
All matches: Phoenix Feather equivalents · Mummy White equivalents