I have php 7.0 running on my ubuntu server.
php -m command says:
[PHP Modules] calendar Core ctype curl date dom exif fileinfo filter ftp gd gettext hash ico
I had the same issue. I fixed it by installing php7.2-xml:
php7.2-xml
$ sudo apt-get install php7.2-xml $ sudo systemctl reload apache2
After that, SimpleXML got listed by php -m:
php -m
$ php -m | grep -i simple SimpleXML