SAFELIGHT
Simple version. Built to be light and reliable on iPhone. Set to play the whole playlist, or add tracks one by one below.
The playlist
Simple intro sound
A short looping tune with no effects. Tap to start. Turn off the iPhone silent switch if you can't hear it.
Off
Tracks, one by one
Paste Spotify track links (one per line). Each track gets its own player. The list is saved on this phone only.