Hi @jester,
before you fix it manually, could you try if the problem auto corrects itself when upgrading the kopano4ucs-webapp package? For this you have to add the following line to /etc/apt/sources.list:
deb http://repo.z-hub.io/kopano4ucs/Univention_4.3/ /
The update then should trigger an updated join script call, which disables php5, enables php7 and restarts apache. I don’t think anything could break from using this package, but its of course always recommended to make a backup first.