The Swiss defender arrives from Fulham.
"He's played for some top sides and was a big influence in Arsenal's run to the Champions League final in 2006, so we're bringing in a really experienced player who's been there and done it, and that will be important for the team," Lambert said.
"I went to Switzerland not long ago to watch the national team train, and I could see he has a good, strong mentality for the game.
"Ottmar knows players, and for him to say that Philippe has never disappointed him on the pitch, that's no small commendation.
"This will be Philippe's third World Cup finals, and there aren't too many players who compete at that level over that stretch of time. He will be a great addition to the group."
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