There is no doubt that Google has made massive progress helping advertisers get a return from users on mobile devices. That being said, a significant percentage of the time, mobiles don’t perform as well as desktops.
If this applies to you and your patience is up with advertising on mobile devices, the above video will show you how to remove them from your campaign.
Where I have added a 100% decrease in bid (this switches off mobile devices), you can add a decrease of less than this e.g. 50%, if you are getting conversions, but not quite at the cost you need.