Apple wants you to upgrade your old iPhone and is willing to give you a bit more trade-in credit to convince you to do so. Until June 3, the Apple Store (both online and physical locations) is offering more money in trade-in value for your old iPhone when you trade it in for a newer iPhone.
The promotion applies to the iPhone 11 and newer, but Apple continues to accept the iPhone 7 Plus or newer for the usual trade-in value. The other thing to note is that you don't need to get the latest iPhone 15 to trigger the credit boost for trade-ins; you just need to get a newer iPhone than the one you're selling.
Although Apple has published the higher values for trade-in credit (anywhere from $10 to $30 more), the ultimate amount Apple offers you will depend on the condition of your phone. You get a preliminary amount when you answer some questions about your device, and Apple will issue you the credit once they receive the device and confirm the description of its quality is accurate.
Here is how much you can get for your iPhone right now:
iPhone 14 Pro Max: Up to $650 (vs. $630)
iPhone 14 Pro: Up to $530 (vs. $520)
iPhone 14 Plus: Up to $430 (vs. $420)
iPhone 14: Up to $380 (vs. $370)
iPhone SE (3rd generation): Up to $170 (vs. $160)
iPhone 13 Pro Max: Up to $460 (vs. $450)
iPhone 13 Pro: Up to $380 (vs. $370)
iPhone 13: Up to $320 (vs. $300)
iPhone 13 mini: Up to $300 (vs. $270)
iPhone 12 Pro Max: Up to $370
iPhone 12 Pro: Up to $300
iPhone 12: Up to $220
iPhone 12 mini: Up to $200
iPhone SE (2nd generation): Up to $90
iPhone 11 Pro Max: Up to $300
iPhone 11 Pro: Up to $250
iPhone 11: Up to $200
iPhone XS Max: Up to $160
iPhone XS: Up to $120
iPhone XR: Up to $120
iPhone X: Up to $110
iPhone 8 Plus: Up to $90
iPhone 8: Up to $60
iPhone 7 Plus: Up to $60
Remember that the boosted credit only kicks in if you are using the credit to upgrade to a newer iPhone. Also, even with the boost, you may be able to find a better trade-in value for your iPhone from third-party retailers like Back Market. Before you finalize the trade-in through Apple, do a quick check with other retailers to see if you could get more money elsewhere.