Jitsi, Nextcloud Talk and Signal are all very good options (if you don’t need screenshare with desktop sound (e.g. a watching a tutorial video with sound), I haven’t found a FOSS solution that can do that - though tbh it’s been a while since I tried it with something other than Signal)
Im petty sure you don’t need to root a phone to install a custom ROM nowadays (unlocking bootloader, yes. And it is obviously more work installing a custom ROM than buying one that comes with it preinstalled).