Yum install php v5.4 packages while I have installed php 7

I have installed PHP version 7 on my centOs. Now I got an error says: > undefined function mb_internal_encoding() So I decided to install php-mbstring (using yum install php-mbstring) but I face the following error: > Error: php70u-common conflicts with php-common-5.4.16-43.el7_4.x86_64 > > Error: php70u-json conflicts with php-common-5.4.16-43.el7_4.x86_64 But now when I install php-mbstring, it wants to install php-mbstring version 5.4. How can I tell yum to download latest versions of php extensions and packages?