From The Windows Phone Developer Blog:

Follow these instructions to simulate IE 10 on Windows 8 Phone.

1. On Windows 8, open Internet Explorer 10.

2. Bring up the IE Developer Tools either by hitting the F12 key, or, on the Tools menu, click F12 Developer Tools.

3. Click Tools, click Change User Agent String, and then click IE10 for Windows Phone 8.

4. To resize the browser window, click Tools, click Resize, and then click 480×800

The UA string of Internet Explorer 10 on Windows Phone 8 will look like the following:

  • Mozilla/5.0 (compatible; MSIE 10.0; Windows Phone 8.0; Trident/6.0; ARM; Touch; IEMobile/10.0; <Manufacturer>; <Device> [;<Operator>])