I had this issue before and now I know how to configure. Here's the solution:
On ePO 5.9.x or 5.10:
1. Go to Policy Catalog > Data Loss Prevetion 11 > Default Windows Cliente Configuration > Plug and Play
You can see the iPhone Protection Mode. Select Block but allow charge.
2. Go to DLP Policy Manager
2.1 Actions > New Rule Set
2.2 Put a name and description
2.3 Open the rule and click Device Control
2.4 Actions >Plug and Play Device Rule
Condition tab:
End-user: is any user (ALL)
and Plug and Play is one of (OR): All apple devices (default)
Exceptions tab:
Enable Excluded Users: End-User belongs to one of end-user groups(OR): put the group from AD allowed to access iPhone storage.
Reaction tab:
Action: Block
User Notification: Put anything that you want to show information
Report Incident: mark the checkbox
Computer disconnected from the corporate network: React the same way as connected system
Computer connected to corporate network using VPN: React the same way as connected system
2.5 Save
2.6 Remember to Change State of the Rule to Enable
2.7 Go back to DLP Policy Manager > Policy Assignment
2.8 Actions > Apply Selected Policies
This will block iPhones for ALL users except people from the group you select, but anyone will be able to charge iPhone on the USB.