Some additional info and my own thoughts on that:

observation returns 0 or 1 to signify the phase, and in phase 1 the dice result
if phase is 0, action 0 is “pass and take your share”, action 1 is “go on”
if phase is 1, action 0-13 is interpreted as a corresponding action in that game

I could easily treat action 2-13 as “no-action” in phase 0, or all of 1-13 as “go on”. But I expect that would make convergence much slower and more unlikely, since the DQN would have to learn these additional unnecessary relations.