It depends on what you want: You could create a website that works well for many clients e.g. by applying the concept of Responsive Design. For the fun of it, got to the site of Sylvester Stallone and resize your browser window to see how the page adapts.
Or you create a website with a strong focus on the mobile (or tablet) device that looks like a native app - then use frameworks like that from Sencha or JQuery Mobile. In this case you go the route of creating something like a Web Application but not a website for the average visitor.
For Sencha: You don't need Architect but it will help you speed up the interface part.
Another way would be a combination, let's say you have Wordpress, choose a Theme that uses responsive layout and install a plugin that delivers another themed variant of the page just for mobile devices.