Hey @lillahelle! This has to do with the way that Spotify is licensed. A Spotify subscription is intended for use by a single individual (family premium being an exception). As a result of this, you are restricted to having only one streaming device at a time on your account. To make this more attractive to the user, Spotify utilizes Spotify Connect to allow you to control the current streaming device from any device on your account.
If you listen on your mobile phone, then log into the desktop app, you should see what is currently playing on your phone, with the option to switch devices if you wish.
I find it quite useful when commuting to and from work. I can listen through my phone while driving, then log into the desktop app when I get to work an easily continue the session, without having to find what I was listening to. It'll even carry over queued songs. I can then do the same at the end of the day when I leave to go home.