OpenWRT Client Mode Scan for other clients in WLAN

I am using LinkIt Smart 7688 - an OpenWRT device for IoT. It supports station mode WiFi i.e. it can connect to another WiFi AP and one can use inteet. I am trying to retrieve a list of mobile phones that are connected to the wireless lan. I am trying to list all the clients but my Android phone is not showing up.

I used nmap with the command

nmap -sP 192.168.0.1-254

and i get this

Starting Nmap 6.47 ( http://nmap.org ) at 2016-06-20 17:44 IST
Nmap scan report for 192.168.0.1
Host is up (0.0049s latency).
MAC Address: F0:7D:68:B8:BB:D0 (D-Link)
Nmap scan report for 192.168.0.6
Host is up (0.0038s latency).
MAC Address: 6C:62:6D:4E:87:28 (Micro-Star INT'L CO.)
Nmap scan report for 192.168.0.12
Host is up (-0.089s latency).
MAC Address: FC:AA:14:B8:12:91 (Giga-byte Technology Co.)
Nmap scan report for 192.168.0.111
Host is up (-0.095s latency).
MAC Address: 40:8D:5C:49:FA:24 (Unknown)

Is the problem related to my phone or are there other tools to do this?