how to apply a recoil pressure in CFD?

I am dealing with laser welding simulation. I use a phase field method to track the vapor/melt interface. I can link the heat source to the interface with delta function, but:

1. how can I apply a recoil pressure on the interface when boiling point is reached to make the interface deform with vaporization?
2. a jump conditon is needed at the interface, linking normal velocities of vapor/melt phases with their densites, how can I do that？