Any phone with Miracast (or AllShare/Samsung Link for Samsung phones) support is able to 'mirror' your phone to your TV. However, not all TV's are capable of this. Same thing with Chromecast; unless you get an app that mirrors your phone as a video feed, you're restricted to media sharing and streaming from apps that support it.
What's your phone model? Do you have a SmartTV (if so, what model) or are you only using Chromecast?
I don't know of an easy or straight-forward way to mirror your phone's screen on the computer.
Does that work both ways?
I think you can stream media from your phone to your laptop using Samsung's software (S-Link I think it's called, don't really remember, they've changed the name so many times already) but I don't know of an easy or straight-forward way to mirror your phone's screen on the computer.
EDIT: I did find this video on YouTube... MAAAAAYBE it'll help. Haven't really tried it myself.
https://www.youtube.com/watch?v=j8foXW5gqbs