Centos 7 php install comes with the ModSecurity package installed and enabled which prevents web access to phpMyAdmin. At the end of phpMyAdmin.conf, you should find
# This configuration prevents mod_security at phpMyAdmin directories from
# filtering SQL etc. This may break your mod_security implementation.
#
#<IfModule mod_security.c>
# <Directory /usr/share/phpMyAdmin/>
# SecRuleInheritance Off
# </Directory>
#</IfModule>
which gives you the answer to the problem. By adding
SecRuleEngine Off
in the block "Directory /usr/share/phpMyAdmin/", you can solve the 'denied access' to phpmyadmin, but you may create security issues.