This question already has an answer here:
I installed Ubuntu Server 19.04 from VirtualBox on Windows Host. I have a terminal screen 800x600. VirtualBox does not provide me an option to change resolution.
How do I change the terminal resolution?
1) Downloaded VirtualBox Guest Additions from virtualbox.org, mounted media, and installed.
2) sudo apt-get install virtualbox-guest-additions-iso
Wonder if the problem is because it's the Server version, and there's no graphic interface or X11.
Guest Additions installed:
$lsmod | grep vboxguest
vboxguest 331776 1
Looks like GRUB might have something to do with it.
Looks like I need a graphical terminal.