It sounds like your laptop's MAC address is whitelisted. I'm surprised that your college won't allow cellular devices to connect to their WiFi network.
MAC addresses are stored in firmware, so it's not something you can easily change. In fact, it's not something that is meant to be changed at all. That's not to say you absolutely can't do it. First of all, you need to jailbreak your iPhone, which will void your warranty. Also, keep in mind that changing your MAC address can cause problems including breaking applications and potentially bricking your iPhone. Note that people who have iOS 9 are reportedly unable to spoof the MAC address.
I would not recommend trying it personally.