The phase keys are defined in src/thermopack_constants.f90, and are stored as attributes of the thermo class. That is, the phase flag for liquid (1) can be accessed as eos.LIQPH from any equation of state object. See Getting started for an introduction on how to initialise an equation of state.

Phase	Value	Code name	Description
Two-phase	0	TWOPH	Liquid-vapor two-phase mixture
Liquid	1	LIQPH	Single phase liquid
Vapor	2	VAPPH	Single phase vapor
Minimum Gibbs	3	MINGIBBSPH	Single phase root with the minimum Gibbs free energy
Single	4	SINGLEPH	Single phase not identified as liquid or vapor
Solid	5	SOLIDPH	Single phase solid
Fake	6	FAKEPH	In rare cases no physical roots exist, and a fake liquid root is returned