It is an application that plays and selects the iPhone standard music player from AppleWatch.

I need AppleWatch (watch OS 4).

[Operation with iPhone]
You will be asked permission to access iPhone's music library the first time you connect AppleWatch's app.
Please allow it.

[Operation with AppleWatch]
Album information on the iPhone side is not automatically acquired.
If necessary, please acquire with the selection track > album acquisition button.
It may take several minutes to get it.