My office server runs 3CX, php7, Wordpress, MySQL, postfix, dovecot, wine, and a pretty GNOME desktop. I assume you use separate configs for 3CX and your other website? I know I do. I will say I don't run ssl on my website.
Running other services on the same server as your phonesystem and especially other webservers/websites is a recipe for disaster and far from ideal. No matter if you are running separate configuration for each server/user, or harden the system overall, you put everything at great risk.