How to listen to iphone 7 music on an airplane

Through the speakers though the other passengers may get annoyed.

Why not use the included earpods with lightning connector or use the included lightning to 3.5mm adapter?

See this -> https://www.apple.com/iphone-7/

EarPods. With a Lightning connector.

iPhone 7 comes with EarPods that have a Lightning connector. But if you still want to listen through your old headphones, you can plug them in using a 3.5 mm headphone jack adapter, also included.

The iPhone 7 includes Earphones that connect to charging port to listen to music. It also includes a lightning port to 3.5mm audio jack adapter so you can use normal earphones with it.

You can use wireless bluetooth headphones as well. Or even just the built in speakers.

So plenty of options without the built in Audio jack.