This stand amplifies your iPhone's music - not tremendously, but noticeably. It includes an opening in the back for the charging cord.

The upper part that holds the phone is parameterized, so you can adapt it to your particular phone model and case. The .STL file is for my iPhone 7 with my specific case. It probably won't be right for yours, so use the Fusion 360 file and set the parameters to your phone & case's measurements.

Mine is an iPhone 7 and the sound holes are aligned with its speakers. Other models of iPhone might need adjustment of the sound holes, but probably not.

I have no idea if this would reusable on things other than iPhones - please comment if it does work for you on some other model.