You can upgrade from a Sim-Only plan to a phone plan provided you've made payments on time and have been with the network for long enough, as well as upgrade from a phone plan to a new phone in the last 30 days without trading in your phone.
If you are on an older All-Rounder or Full Works phone plan there was the option of "Upgrade Anytime" which allowed you to upgrade to another phone plan within the 24 months but this requires trading in the phone and/or paying an appropriate early upgrade fee to keep your existing phone.
