Can I sell my iPhone to Apple

No. Apple will not buy the iPhone from you for cash.

They will take in as trade in and apply its value towards a purchase of a new device to lower its price, or give you a gift card you can use to buy anything from an Apple Store, but will not give you cash for it.

Apple has a trade in program, yes. See more here:

https://www.apple.com/shop/trade-in