Hello!

Your tax rate setting is stored on Square's servers, rather than on each individual device. If multiple devices are signed into the same Square account, the same tax rate will be applied to each device. If you make a change to your taxes on the Square dashboard, it will be reflected on all devices that are signed in.

Since you can apply taxes to specific items, one workaround that comes to mind is creating two sets of items, one for your stand and one for your phone.

This would allow you to only tax the items you'll be selling on the Square Stand.