I would not do that. Once you have opened the phone, Apple will not touch it anymore, even if you are willing to pay the OOW-Service fee.
If only the glass of the screen is broken, Apple will only replace the screen, not the whole unit.
Maybe you should talk to Apple Support or Authorized Apple Service Provider to clear that up, and not to an Apple Retailer. ( who would rather wants to sell you a new phone 😉)
iPhone - Contact Support - Apple Support
Repair and replacement costs depend on your iPhone model and your AppleCare product coverage. Apple will run a diagnostic test to determine whether your iPhone has experienced additional damage. If it has, or if it needs other repairs, you may need to pay an out-of-warranty service fee. Accidental damage isn't covered under the Apple One Year Limited Warranty.
Model |
Screen repair service fee |
iPhone 6 |
A$ 148.95 |
iPhone 6 Plus, iPhone 5s, iPhone 5c, iPhone 5 |
A$ 178.95 |
The screen repair service fee includes a A$ 19.95 shipping fee. All fees are in Australian dollars and include GST. Pricing may vary for screen repair service through an Apple Authorized Service Provider or your wireless carrier.
copied from Service Answer Center - iPhone /Australia