Most of the time when people think someone is mafia, they are wrong. Most of the time town will waste two lynches on one person rather than just one, if phoenix is in the game. The best thing to do as town is try to kill off all but one mafia member, then kill the phoenix. If the game doesn't end, the phoenix is town. If a player is 100% confirmed mafia with phoenix at the start of the game, it may even be a good idea to not lynch them until all other mafia members are dead. You can gain information via their votes, and then when the other mafias are dead you won't have to lynch the phoenix twice.