Connecting headphones to Android cell involuntarily transfers sound to that cell from speakers/lapto

[yayoikusama]

Plan

Premium through family plan

Country

Sweden

Device

Samsung Galaxy S6, HP Laptop

Operating System

Android 7.0, Windows 10 Home

My Question or Issue

Since a couple of weeks Spotify automatically transfers music audio from playing on my laptop/speakers to my cell phone when I connect headphones to that cell. It's very annoying since I use headphones when talking on the phone. This hasn't been a problem before, and I cannot remember changing any settings in Spotify or on my Android device. How can I deactivate this?