Hi,
Is there a single command you can use within FreePBX to expand the disk space within the container, after upgrading the container on VULTR?
Thanks in advance for any pointers
No, you cant resize a mounted ext partition safely , l believe the Archlinux iso they offer has gparted and clonezilla on its live desktop
So there is literally no way to resize a FreePBX partition once installed? 
Not quite true, but unless your bash fu is exceptional and you have nerves of steel I suggest you go the alternative live linux boot iso route.
Just try it, take a snapshot (in case) , boot the Archlinux iso, gparted your /dev/vda remove the iso , it will reboot into your resized machine.
How risky (out of 10) would you say doing it the gparted route is?
Is it pretty reliable? Or can it cause large system bugs / issues in the future?
0 risky, no issues. Just a gui wrapper around parted.
Ah fine, I misunderstood. So it was just if it’s mounted it becomes an issue then?
If I power down out of hours, and run it via gParted, I will be able to extend the partition flawlessly?
Provided you don’t press the wrong button twice , its pretty idiot proof otherwise
Something to keep in mind, last time I did it using gparted. I had to delete the swap partition to expand the primary partition. I then added a swap file once expanded.
There is more then one way to skin a cat, that was just my experience.
If you do have a swap partition, you can just move it to the end of the disk to enable the expansion, it is easier and can be done in the GUI without needing dd/makeswap/edit fstab/mount