ΔE 12.7, fair: the same colour family, but not a straight swap. Phoenix Orange is a little lighter, more muted than Ryza Rust. They are different kinds of paint: Citadel Ryza Rust is an opaque base/layer paint and Green Stuff World Phoenix Orange is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Phoenix Orange is a little lighter, more muted than Ryza Rust. They are different kinds of paint.
The same difference applies the other way round: Ryza Rust is a little 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 Ryza Rust on the colour wheel See Phoenix Orange on the colour wheel
All matches: Ryza Rust equivalents · Phoenix Orange equivalents