I don't use much "screen mirroring"... but I think of it as a way to bluetooth connect between my phone and my smart TV. Maybe there are other applications too, but I just don't do much of this sort of thing.
What you may be asking about, instead, is "remote desktop." This is a very similar thing (in my mind)... so that you could control your Kubuntu Linux from another computer (or even from your phone). The app I use for this is TeamViewer... but I have never used it with a phone. Personally, I don't trust phones too much, and anything with remote connection capability to your home computer should be thoughtfully considered for the risk it presents.
Remote desktop is a great troubleshooting tool for helping people who live too far away, and there are other ways of doing remote desktop besides TeamViewer... but TeamViewer makes it very easy. If you decide to test it, you need to use the same version on each device that you will connect. I am still using version 12 and have never upgraded to v13, so I don't know about it specifically.
There are also screencasting programs like OBS Studio that will allow you to create a video stream of your desktop - but I think the streaming functionality requires a connection to some kind of web-based streaming service (e.g. twitch.tv, facebook live etc).
OBS should be available in the *buntu repos.
Offhand, I'm not sure whether OBS Studio allows you to create a localised stream on your local wifi network or not. So the downside to this approach is that your stream could be broadcast to anybody listening on the internet! :/
Another option (albeit a much more expensive option) might be to consider using something like wireless HDMI Extenders.
These things are quite expensive and aren't completely wireless, because they require two short HDMI cables (one to connect your TV to one of the extenders and the other to connect your laptop to the other extender). I think the extenders each have a power supply too - so there would also be a power cable required for each extender.
Although not a completely wireless solution - it at least means that you could use your TV as a second monitor on your Linux PC and you can have your PC further away than you could with a direct, cabled HDMI connection. (Typically HDMI cables are no longer than 2 or 3 metres - So with a cable your PC would have to be pretty close to the TV.)
By using a wireless HDMI extender, you could have your PC virtually anywhere in the house. It wouldn't be a particularly portable setup, but wireless HDMI extenders might be worth the expense if the setup will be a permanent thing - e.g. the PC in question is always going to be situated in exactly the same place.
So there are advantages and disadvantages to each option.
Personally, whenever I want to connect my Linux laptop to the TV in the living room, I just use a 2 metre long HDMI cable. Not at all wireless, but it's the simplest, cheapest and most direct solution for me!
After connecting my laptop to the TV, it's just a case of opening the KDE settings dialog and enabling the TV in the monitor settings page.
Also in the "audio hardware" settings tab of the audio settings page - change "full stereo duplex" to "HDMI output" to route all sound from your laptop to your TV.
If I understood, you want to mirror content like Netflix, Amazon Prime Video, Crackle, HBO Go and YouTube from your Linux PC to your TV, right? Whell, if this is the case, the best option is to mirror this content through Chromecast using Chrome browser. Recent versions of Chrome (and Chromium) have the option "Cast" in the Main Menu (the three vertical dots in browser window top right). Alternatively you can access the "Cast" feature by right clicking in the page body. Chromium can easily mirror the whole desktop. To do this you just have to click in the "Cast Icon" that apears after you start to cast, click in the arrow next to "Cast to" and Select "Desktop" instead of "Browser".
If you want to cast other contents, like a video file in your system, you should install mkchromecast. For more information on how to install an use mkchromecast, visit the official page of the project <a href="http://mkchromecast.com">here</a>.
If you have Google Chrome as a browser you can go to the more menu (...) > cast > select a device to cast to (only some displays can only receive specific video website' content, not a full desktop stream).