Sorry, I may make up something. I suspect that my boss just compile the source code of Apache but used yum to install the php modules. My boss prefers to compile source code because he said that this will allow him to upgrade the system version.
[root@moodle2test ~]# yum list php-xml
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: ftp.cuhk.edu.hk
* epel: mirrors.aliyun.com
* extras: ftp.cuhk.edu.hk
* remi-php72: ftp.riken.jp
* remi-safe: ftp.riken.jp
* updates: ftp.cuhk.edu.hk
php-xml.x86_64 7.2.16-1.el7.remi @remi-php72
If you have no idea, I may give up. Thank for very much for your help.