epi-phase

https://doi.org/10.1351/goldbook.E02168
The less dense phase in a distribution system. The term is often used when two non-aqueous phases are present or when the solvent is an aqueous solution.
See also:
hypo-phase
Source:
PAC, 1993, 65, 2373. (Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)) on page 2380 [Terms] [Paper]