Thanks, I see now it gives an example of how to start a number and there's no + sign before the country code so I guess "Use only numbers" means just that.
That's correct, you don't need the +. The + sign is used because not all countries follow the ITU recommended 00 dial out code, eg Japan uses 010. In this case, you don't know which country we are dialling from and we know all numbers are international so the + is superfluous.