Windows – How to see the negotiated wireless speed in Windows 7 and OS X

Because you mention that it works better in Windows 8, it could be a driver problem. Make sure you have up-to-date windows updates, including optional updates which sometimes have vendor specific hardware updates. Try locating your network adapter in your device manager, right clicking the adapter and select "Update driver software..." If this is already up to date, try uninstalling and reinstalling the driver. If this is a dongle and not internal card try searching for the driver directly from the manufacturer.

Not getting the full speed on WiFi might be due to a lot of things.

You can check your link-speed. If it is not 54Mbps (but far below that) you might have a lot of interference in the air. But your phone has good speed so your laptop should be able to get the same.

You can try switching to 802.11g (instead of the 11b/g/n mixed mode). 802.11n is of no use for you with the limited internet speed and 802.11b is probably not used.

Setting it to 802.11g can give you some stability (depending on the router). (it usually does for me) When you do have a modern-modem you could try 802.11n only but if you see your link speed at 65Mbps with that mode it might be better to choose 802.11g for stability because your modem does not give you the full 802.11n speeds.

Also use a reliable (and several/different) speedtests because they can vary greatly. For example with some speedtest i get 5Mbps while i have 150Mbps. http://www.speedtest.net works nicely for me. They also have a mobile app (http://www.speedtest.net/mobile) so you can compare the phone speed to you laptop.

(The app for Windows Phone should be here, there is a link to the store on the mobile page mentioned above)