You can roll over small sums every year, but the rollover will come from both previously deducted (which you pay tax on) and non deductible (only pay tax on the gains between contribution and rollover) in proportion to the balance of each. The only way to move the whole $5500 non-deductible contribution is to also move all of the previously deducted balance (and pay tax on it). This isn't usually ideal because the fact that you can't contribute directly to Roth means you're in a relatively high tax bracket now, so you'll probably be in a lower tax bracket when you stop working, so you should wait and convert then. Usually the advice if you have existing deducted IRA balances is to just skip IRAs and invest in taxable.
You might still have a couple of options though. You could check and see if your current 401k allows incoming rollovers from rollover IRAs. If it does, and the investment options are acceptable you could roll over the IRA and then proceed with the backdoor Roth.
Also, IRA's are individual accounts, so if your spouse doesn't have any previously deducted IRA balances (s)he can still do a backdoor Roth even if you can't.
The Madfientist link is describing something different than a backdoor Roth. He's describing a process that you might consider once you're in a lower tax bracket (probably in retirement) of rolling over previously deducted IRA funds to Roth and paying the tax. Then, once five years has passed you can withdraw these rollovers (but not gains on the rollovers) without paying tax or penalty. It's a way of getting around the penalties for withdrawing IRA funds before the age of 59.5. This one is commonly called a Roth conversion ladder.
I know all this stuff can be confusing, but I'm sure you'll get it, and if not, post more questions.