CRA requires that the tax on the full value of the item be submitted when the item is delivered. It's not like a lease or rental where the tax is only on the monthly amount because you don't own the item in that scenario. You can consider your monthly amount as a loan repayment just like if you took a loan out from the bank to buy the phone. You still need to pay the full tax on the phone up front when you buy it regardless of how you pay it off.
