Welcome to the Community.
We do not currently offer shared plans. However each phone can have their own plan with data. You can check out all of our available plans right from here.
As for changing your plan and getting a new phone; you can do this by logging into My Account and clicking on > Usage & Services > Mobile > Selecting your Phone number > Clicking on ``Upgrade My Device``.
After selecting your phone, you'll be prompted to set-up the plan change.
I hope this helps.