Phones don't have an SSID number that you can use. In the possible case, you can check the SSID name of the WiFi network you connect to. If it's an Android phone, go to Settings > Wireless and network > Wireless.
If you turn on the hotspot feature, you can configure the SSID from the same menu where you've activated it. You can change the SSID, password and encryption.
There is no way to find the SSID for the given phone. Additionally, go to Settings > About Phone to find more information about it.