When accessing phpmyadmin in docker, source ip would be '172.17.0.1', not '127.0.0.1'. So what you have to do is in '/etc/httpd/conf.d/phpMyAdmin.conf', either change 'Require ip 127.0.0.1' to 'Require ip 172.17.0.1', or to 'Require all granted'.
(original)
AddDefaultCharset UTF-8 <IfModule mod_authz_core.c> # Apache 2.4 <RequireAny> Require ip 127.0.0.1 Require ip ::1 </RequireAny> </IfModule>
(revised)
AddDefaultCharset UTF-8 <IfModule mod_authz_core.c> # Apache 2.4 <RequireAny> #Require ip 127.0.0.1 #Require ip ::1 Require all granted </RequireAny> </IfModule>
Do not forget restart httpd!