this is hard to follow, it's probably easier to focus on Form 8606
are you doing the Roth conversion part of the backdoor? the basis should not be rolling and growing.
if you're doing backdoor Roth you should have a non-deductible contribution and a Roth conversion (reported on 1099-R), the basis should be zero at the end of this assuming you have no other pre-tax earnings in your IRA and bring the Trad IRA balance to zero. There shouldn't be a rolling basis, unless you make the contribution after year-end for the prior tax year then all you report is the contribution which carries forward to the next year and the conversion is reported in that calendar year it's performed.
the most common issue I've seen reported here is folks don't identify the 1099-R as a Roth conversion properly in the questions which follow the form entry.
here are the steps for backdoor Roth in turbotax
https://ttlc.intuit.com/turbotax-support/en-us/help-article/retirement-benefits/enter-backdoor-roth-...
