It could be just your connection is down or there could be a routing issue.
I can load the website just fine on my iPhone and on my desktop computer.
Sometimes ISP's have a routing issue that allows you to connect to some websites and not another.
So if you're connecting through your phones internet connection and it cannot get to the website then it could be an issue with the ISP.
But if you're connecting through WiFi and you cannot connect with your phone but can do so on your computer through the same ISP then it could be an issue with your phone.