Request desktop site.
For iOS 8 tap Safari's URL bar and then pull down to reveal the Request Desktop Site option.
For iOS 9 Simply tap and hold the refresh icon in the URL bar and select 'Request Desktop Site'
Tap the top right menu icon (three vertical dots) and choose 'Request Desktop Site'
Why do you want the desktop site?
Before you do - would you mind letting us know why you want the desktop site on your mobile so we can make sure we bring any missing features or functionality to the mobile version as soon as possible.