When playing Phase 10 with 2 or more players, how do we conclude the hand?
Score is used when more than 1 player completes Phase 10 in the same hand. Completing a phase doesn't end the hand immediately; a player must go out by getting rid of all his or her cards. So a second player can complete Phase 10 after the first player has done so. Once a player goes out by getting rid of all of his or her cards; then if multiple players have completed Phase 10; score is used to determine winner.


  GOING OUT: The player who gets rid of the last card in hand, by discarding or hitting, is said to go out. This player wins the hand. The winner of the hand, and any other players who also complete their Phase, will advance to the next Phase for the next hand.


and


  If two or more players complete Phase 10 in the same hand, then the player with the fewest total points is the winner.


http://www.natlassoc.org/fun/games/phase10/phase10r.htm

Note that the terminology is a little confusing, because the rules say that whoever goes out "wins the hand", but "winning" the hand doesn't really mean anything other than getting 0 points for that hand. Anyone who completed the Phase moves on; and "winning" Phase 10 doesn't mean that you will win the game.