I bought a new phone with Type-C port and supports 25W fast charge. As you know, they no longer send adapters with new phones.
My laptop also has a Type-C port (so I am using type-c to type-c cable) and turns out my laptop can charge my phone at 25W.
I use my laptop plugged-in(battery conversion mode at %80) and my question is will it damage the battery of my laptop or phone in the long run?
No. The laptop is made to discharge at that and higher wattages and the phone to charge at that wattage but no more, don’t worry however, the laptop and phone communicate for wattage, and if they can’t it’ll charge it slow (5W)