Phalanx Yellow vs Moldy Ochre

How close are they?

ΔE 16.5, loose: different enough that you should pick on purpose. Moldy Ochre is noticeably darker, more muted than Phalanx Yellow.

Can I use Moldy Ochre instead of Phalanx Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Moldy Ochre is noticeably darker, more muted than Phalanx Yellow.

Can I use Phalanx Yellow instead of Moldy Ochre?

The same difference applies the other way round: Phalanx Yellow is noticeably lighter, 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.