Set a PIN or passcode: This is the first line of defense—if someone wants to access the device, they first need to break the code. With Office 365 subscriptions, the administrator can preset the accounts to require a 4-digit pin to be added to any mobile device, in order to have the Office 365 account added to that device. If your team uses a different email platform, consider asking the administrator to add this capability.
Use remote locate tools: Several software solutions help locate lost or stolen devices
through GPS and geofencing capabilities. iPhones have a built-in utility called "Find my iPhone" and you can upgrade that to a more serious MDM solution through your IT department, with features like Remote Wipe.
Keep devices clean: Phones are mini-computers, and just like “big” computers, they need to be cleaned up from time-to-time. Utilizing an antivirus and malware scanner is always a good idea, but more importantly, employees should be encouraged to only ever install software needed for their job productivity – not "fun." That's the best way to avoid the infected applications.