The backdoor method is actually to separate transactions, a traditional IRA contribution and a Roth conversion.
Yes, if you made a traditional IRA contribution form 2017 you must report it on your 2017 tax return. As a nondeductible contribution, it will be reported on 2017 Form 8606 and will appear in the total on line 14 to carry forward to line 2 of your 2018 Form 8606.
A Roth conversion is performed in a particular year, not for a particular year. Your Roth conversion performed in 2018 is reportable on your 2018 tax return, not on your 2017 tax return. The taxable amount of your 2018 Roth conversions will be calculated on your 2018 Form 8606.
