GDPR and the phone app

I have a real concern that at present the phone app could be accessed by persons other than the member of staff it is assigned to. If someone was to pick up their phone, there is a chance they could open the app and see confidential items including addresses and key safe numbers. I know staff should be vigilant but it only takes one instance of this to put an already vulnerable person at a high risk of abuse.

Please let me know if there is a default setting that would mean my staff would need to log on/off with a password at each call, or if there is a simpler solution to what could become a very real threat.