Can't create virtual screen (Trying to use a mobile as a secondary screen)

I was trying to use my phone as secondary monitor using VirtScreen but it shows “No virtual screen name found”.
I am guessing that I need to make a virtual screen that will be mirrored using vnc.
So how does one create a virtual screen.

I just did it. with an integrated intel card…
You need ne kernel module vkms:
How to load vkms-Module.
Then you can use arandr, a gui tool, to open a screen with the name of virtual.

If you are using the nvidia, this migth help:
Add: /usr/share/X11/xorg.conf.d/30-virtscreen.conf

# nvidia/nouveau/amdgpu device should be configured first before Intel GPU
Section "Device"
	Identifier "nvidiagpu0"
	Driver     "nvidia" # Because you are using Nvidia proprietary driver. Change to "nouveau" if you are using open source nouveau driver

# Then configure intel internal GPU
Section "Device"
	Identifier "intelgpu0"
	Driver     "intel"
	# You may put Option "VirtualHeads" "1" here but it seem you don't need to put this for Ubuntu 18.04.

Source: VIRTUAL1 option not available-Github