Why is it relevant if the guy kept the phone or not? He may have returned his £600 phone and bought a different £16,000 phone - there's no way you know whether or not he can afford things or not.
Why can't he move money from his savings? Maybe his savings are in a notice account which can't be touched? Why is it any of your business how he manages his finances?
As mentioned earlier, Amazon took money from his account in error - Amazon are at fault here.
It's relevant because based on the information he provided, it's clear he's not very sensible when he comes to his finances.
Had he kept the phone, he would still have £600 less in his account and therefore not enough money to cover his financial commitments.
Why would a long term savings account where you're not allowed to withdraw, absolve him of responsibility? He would have known his savings aren't available and therefore he should take more responsibility of his current account.
Yes, Amazon are at fault but that's not the issue. Replace Amazon with a multitude of other scenarios where living hand to mouth will catch you out, and the result will be the same. What if tomorrow he wakes up and no longer has a job because of redundancy? Sensible people ensure they have multiple month's worth of easy access savings available to cover such times.
Oh and before you undoubtedly chime in with "not everyone is so fortunate", do remember we're talking about someone buying a £600 phone.