This appears to be a situation where locally connected devices i.e: a neighbour's phone may be shown in your network. This is not a security problem. As long as your internet connection is protected you should not be able to access the phone's files and it can't access any of yours.
For further information please see the last response (chev65) at http://www.eightforums.com/network-sharing/12630-someones-phone-connected-my-network-why-how-5.html.
Please let me know if this helps address your concerns.