The 2 most common exceptions to the warrant requirement are 1) plain view and 2) consent. The 2, however, are mutually exclusive as it is now, other than when an object in plain view is spotted by an officer who then points out his findings to the suspect who then consents to a more thorough and inclusive search, knowing that a warrant will follow, in short order, based on the plain view findings - ok fine.
What we have now, with this technology (it's not new, BTW my Galaxy Zoom had this 4 years ago) are situations where officers can unscrupulously 'invite'  consent by saying that the password was in plain view...
My analogy: A cop walks up to your front door, which is closed. He can't see anything, so nothing is in view. He can't manipulate the door open; However, if, as he is walking up, a gust of wind blows the door open, then whatever he can see is fair game. By moving the phone, the officer's manipulation is akin to pushing the door making the 'consent' nonexistent and involuntary