I haven’t followed game news much recently, connecting Steam acc to play on mobile phone is still not possible?
You can’t connect it to play on both. You can swap your Steam account to a mobile account though, by opening a ticket with customer support, but obviously that means you can’t play on Steam on that account afterwards.
I am sorry to say that this is no longer possible. I remembered this being the case in the past, but I just filed a ticket last week, and CS told me it is neither possible nor is it planned.
Reasoning behind it is that mobile users and steam users data are stored on different servers and cannot be moved.
Then my thread got moved to suggestions and buried 
But do let me know if you get more lucky than I am.
Then looks like instead of continuing to play this game on the phone I can just quit it.