Electronic devices are permitted, but players may not use them to access information that contains substantial strategic advice.
With the MTG companion App, Wizards has finally had to open up its electronic policy. Mobile devices are a fact of life now. We can only mitigate what they are used for.
For events that use digital decklists, players may only access the decklists of other players prior to the start of a game or in between games. Digital decklists may not be referenced during games.
There are some events that use digital tools and allow you to access your opponents decklist. If you are in an event that makes this available, your opponents decklist is considered an outside note, and must be put away at the beginning of the first game. Accessing the decklist during the game is treated the same as if you accessed outside notes during a game with respect to the recognition of an infraction being committed
Device use during a match other than brief personal calls must be visible to all players. Players wishing to view information privately on electronic devices during matches must request permission from a judge.
Sometimes an opponent is a first responder, or they have a pregnant spouse, or a sick family member. Magic isn’t as important as those things. However, the call must still be visible to the opponent so that they know you aren’t cheating. If the nature of the call is private, speak to a judge in advance.
At Competitive and Professional Rules Enforcement Level during drafting and deck construction, players may not use electronic devices capable of taking and storing notes, communicating with other people, or accessing the internet.
At this moment, you aren’t tracking your life, or looking up gatherer text. So your need to use your mobile device is nearly zero for legitimate purposes. Again, if you need to take an emergency call, involve a judge.
The Head Judge or Tournament Organizer of a tournament may further restrict or forbid the use of electronic devices during matches.
The Head Judge, as always, has final authority on what is allowed, and can forbid players from being able to use electronic devices if they see fit.