This was a particularly concerning case: https://www.theverge.com/2017/2/12/14583124/nasa-sidd-bikkan...

    Bikkannavar says he was detained by US Customs and Border Patrol and
    pressured to give the CBP agents his phone and access PIN. Since the phone
    was issued by NASA, it may have contained sensitive material that wasn’t
    supposed to be shared. Bikkannavar’s phone was returned to him after it was
    searched by CBP, but he doesn’t know exactly what information officials
    might have taken from the device.

Once he unlocked his phone, they were gone with it for 40 minutes. Plenty of time to copy the device contents and peruse at their leisure.