If two players want to co-operate in a game they need to share information and to co-ordinate their actions so that their ships and planets work with each other. PHost implements several features to support co-operative play.

PHost supports formal alliances between players by modifying its behavior as necessary in order to enable the allies to easily co-operate. Thus, allies can fly through each other's minefields (without matching friendly codes), allies can avoid fighting each other in combat (without matching friendly codes), allies can see each other's ships, and so on. Moreover, each of these alliance features can be tailored for each alliance so that different levels of trust and co-operation can be established. Team games especially benefit from PHost's implementation of alliances.

PHost also offers a number of features for players to co-operate without explicitly forming an alliance.