Q: Airport is not allowing connection to a specific website

I have narrowed down my problem to my airport. There is one website I visit and use regularly until the end of last week. Now I get a timed out message on all browsers on all my devices. If I turn off wi-fi on my iphone, the website comes up instantly. Turn wi-fi back on, page won't load. My final test - I connected my iMac to my modem via ethernet. Again, the page loads perfectly. No problem. So my questions are what happened and what do I do to fix it?

Thanks