11.3.b. During play, a player is forbidden to have a mobile phone and/or other device capable of
processing or transmitting chess analysis
in the playing venue. If it is evident that a player brought
such a device into the playing venue, he shall lose the game. The opponent shall win. The rules of a
competition may specify a different, less severe, penalty.
I'd also imagine that this rule's enforcement would be relaxed when, for instance, a player sets up a phone to record the game and has no access to that phone during the game, since any information the phone is recording (and any resulting processing for cheating) would be inaccessible to the user during the game.
I guess this may vary by country, but at least in the USA, phones have been banned in every "novice" tournament that I've participated in. Even books are off limits.