Speed Test, Different Results?

If I go to my SpeedTest app on my iPhone I get 31.10mps download, If I go to their website on my PC it says I get 2mps. What is going on?

Added (1). Only 3G on my phone but using the Wi-Fi and we're told we should be getting around 30ish mps but my PC isn't receiving it for some reason

Does your phone have 4g service? Do you have DSL connected to the PC? If both are yes, the results may be right.