Hi yourxp,
QCD and A.Lab will only replace your iPhone if your device isn't repairable / the following same function is faulty upon repairing twice.
Example: If you have an unresponsible home button / flickering screen or faulty camera, Apple will cover and pay both Parts and Labour for QCD/A.Lab to REPAIR your iPhone under your Apple Limited Warranty.
Example: If your phone's Wi-Fi, Bluetooth, SIM Card ;etc unable to detect (for intermittent issue, the Engineering team in the AASP will diagnose and see if they manage to replicate the issue before granting a replacement.), your phone is entitled to an 1-1 exchange if there's no sign of any unauthorised modification, tampering or any cosmetic damages.
Cheers.