As mentioned by Shaikhhashim2 in earlier answer it could be the MAC based authentication. Your college has given the laptops and they might be using mac address based authentication . MAC address is unique identifier of your device ( here the laptop's wireless card's MAC ID). But in my opinion if you have mac based authentication then your laptop will/may not get IP address.
There is one other method of authentication where access is given based on OS of device e.g only windows 8/10 devices are allowed.
Please check if your laptops's browser is configured to use proxy server. If yes, try to put same setting in your phone too.