In the olden days people use their phone to make phone calls. These days people use their phones for many other things, and if you have a smart (so-called) phone you may well use it to text, email, face-book, twitter, bank, take photos, watch You-Tube, maintain a contact list, manage a calendar, play games, GPS device, and a whole range of applications beyond the scope of my imagination, and of course run goggle web searches and browse the internet.
There have been a number of approaches taken to resolving a website for a phone, (or one of the other devices that are now used for web browsing. The current solution, which seems to have gained enough traction to be normal is based on a Twitter bootstrap, whereby the page is divided into 12 parts, and each block is defined by the number of parts and stacked accordingly.
This site is using a Responsive Theme th some modifications so if you compare how the site looks on a Smart Phone, a Tablet and a computer you will see how the sites resolves itself according to the device that is being used to browse the site. This is quite different to the earlier method of have many various style sheets designed to meet the variances.
One of the big changes that the plethora of devises adds to the mix is that it is no longer all that effective to be spelling out to many dissensions as absolute values, and percentage and Ems have come into their own as being more powerful and helpful for maintaining readability across devices.