- Go in the game folder directory (default is : X:\Steam\steamapps\common\Phantasmagoria 2), then go into the "Phant2" then "DOSBOX" sub-directories.

- Open the "dosboxPHANT2.conf" file with a text editor.

- Search for the line "output=overlay" and replace the "overlay" value with "opengl".

- Once the new line now display "output=opengl", save the change and close your text editor.

- Run the game and now, Steam Overlay should be working.

Note : In old games running under DosBox, Steam Overlay is often a bit laggy (and will be display at the game resolution) but it's still interesting if you want to take screenshots of the game. Screenshots can also be a bit laggy and take a few seconds to be created.

You can also use "openglnb" instead of "opengl", which seems to make the overlay a bit less laggy as this option doesn't use bilinear filtering.