hello,it seems its working as its suppose to work ,I followed instruction here Display-o-Tron: toy music player with scrolling colors Mine works same way and I knew it would after i read those instructions …If you need to use the default sound device i would suggest maybe install raspbian on another microSD card ,and swap back and forth ,or use another Pi Zero .
I built mine knowing i wanted a Pi zero mp3 player, i didnt know at first it was going to work the way it does after doing the install of the phat