The interchange of the denser and less dense phases due to changes in solute concentration. phase inversion is often used in this context but is ambiguous.
See: phase inversion
Source:
PAC, 1993, 65, 2373. 'Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)' on page 2387 (https://doi.org/10.1351/pac199365112373)