Hello, just a quick solution to install php-mssql module in Centos 7.2 with PHP 5.4.16 in Plesk 12.5 and you don't need to enable nothing else.
yum -y install yum-plugin-priorities
sed -i -e "s/\]$/\]\npriority=1/g" /etc/yum.repos.d/CentOS-Base.repo
yum -y install epel-release
sed -i -e "s/enabled=1/enabled=0/g" /etc/yum.repos.d/epel.repo
yum --enablerepo=epel -y install php-mssql
with this simply method, you only install php-mssql module without the risk to update the whole Centos with epel repo, it exclude all packages from update.
Hope it helps.
Best regards,
Horacio Stolovitzky