The enthalpy associated with any phase change can be experimentally quantified and tabulated. Each particular phase change has an associated heat and is given a particular name.
For example, the enthalpy change for melting is defined as the enthalpy change for changing from a solid to a liquid at the melting temperature. For water this would be
\[ \rm H_2O(s, 0^{\circ}C) \rightarrow H_2O(l, 0^{\circ}C) \]
The process of going from solid to liquid is referred to a "fusion". The enthalpy for this change is \(\Delta H_{fusion}\). This a change in enthalpy,
\[\Delta H_{fusion} = H_f - H_i = H_{liquid} - H_{solid}\]
Because of this, the enthalpy for the opposite process, freezing, will be exactly equal but opposition in sign.
\[\Delta H_{freezing} = H_{solid} - H_{liquid} = -\Delta H_{fusion}\].
This means that only one value is ever tabulated. Typically it is the endothermic process. Thus, for solid/liquids the fusion value is tabulated. For liquids/gases you will find tabulated data for \(\Delta H_{vaporization}\). Again for the opposition process (gas to a liquid) the enthalpy is equal by opposite in sign.
\[\Delta H_{vaporization} = -\Delta H_{condensation}\]
.The same follows for the solid/gas phase transitions of sublimation (solid to gas) and deposition (gas to solid).
\[\Delta H_{sublimation} = -\Delta H_{deposition}\]
.