If you are installing new Ubuntu 16.04 LTS or upgrading/Downgrade from your older Ubuntu installation then you will get an error like “phpMyAdmin – Error – The mbstring extension is missing. Please check your PHP configuration”. This error can happen on browser for your phpmyadmin access after installation or upgrade to Ubuntu 16.04.

just run these command

sudo apt-get install phpmyadmin php-mbstring php-gettext

sudo service apache2 restart