MBstring stands for multi-byte string which is used to support ASCII strings. It’s an extension in PHP.
There is a simple solution to resolve this issue is to install the PHP-mbstring in redhat. Download it from here php-mbstring
I have downloaded php-mbstring-5.4.16-45.el7.x86_64 according to your architecture.
Command is yum install php-mbstring-5.4.16-45.el7.x86_64 –y
After installing these packages you will be able to run this commands. There will be no error about php.
yum install zabbix-server-mysql zabbix-web-mysql zabbix-agent