Playing local audio from an Apple phone
What I do in a similar case (iPhone5s &lt;--> Linux):


on the phone, download the free version of FE File Explorer app
open FE, create a folder in Local > On My iPhone
connect the phone to the computer using usb
copy files from the computer to the folder in FE on the phone
in FE, click an audio file to play


(3) works out of the box on Ubuntu MATE 18.04. On an older Ubuntu version, I have to use wifi and samba for file transfer.