Wi-Fi, smartphone,?

I'm using a LG K51s smartphone. Unfortunately the connection to the internet is very bad, pages take forever to load. If I use the mobile version, i.e. Via the SIM card, everything is fine. My laptop is also connected to the router and the internet works fine there. Where could the problem now lie that the connection from the router to the smartphone is so miserable. When I was in the hospital for a few days, there was also internet there, and the internet worked wonderfully there.

All devices have a certain transmission and reception strength. You can't change that.