That's not what a monopoly means, yeah you can buy an iPhone but Android has 75% market share in Europe, that's why it's a monopoly.
The profit isn't from the direct sale of an Android device, it's from the system the device is a gateway to.
Like, own all cinemas in a country but home-viewing keeps profit low, so now it's fine to only allow people to visit your cinemas if they buy clothes from your clothing company?
Edit:perfect->problem