Taxes on iPhone upgrade

So based on what you are saying, assuming the trade in value of my year old iPhone is at least as much as what I owe on the Citizens One loan, I would be better off paying off Citizens directly in full and then trading in the iPhone (now mine) to Apple and starting a new agreement, since they then would credit my card for the trade-in value plus tax on that amount.

I was charged sales tax (in Pennsylvania) on the full price of my new phone purchased through the Apple program. However, since I owned the previous phone, I guess Apple was allowed to treat the trade-in value as a "refund" of sorts, and therefore, the tax on the refund price was also returned to me, just as if had I purchased the phone outright and returned it to the store within 14 days, the purchase price and sales tax would have been refunded 100%. So the question is if I return this phone after one year, does Apple effectively refund me half the price of the phone (and forward that refund to Citizen's to pay off the balance) thereby allowing a refund of half the tax, or would I need to buy the phone off of Citizen's and turn around and trade it in to Apple as a new, separate agreement?