I assume you are referring to the Windows/Mac desktop app. If so, open the settings by click on the "Gear" icon in the lower right hand corner of the app. Then select the top menu option entitled "Calling". The select "RingOut" (the 5th option down) and enter your cell phone number. That will allow you to call out from your cell phone rather than a direct dial out from the application.
OK...Open settings by clicking on the 3 lines in the upper left corner of the app. Then click on "Settings" (second menu option from the bottom). Select the first option "My Mobile App Settings" and then select "VOIP Calling". You will need to disable the "VOIP Calls" and "Over 3G/4G" (and Incoming VOIP Calls if you want to use your cell phone to receive calls too). You will also want to check the "RingOut Mode" selection to make sure that your Android phone is the one you will be calling out from.