Change 8080 to 80 its the default. But if you want your site to run on 8080, then you have to use it. Another solution might be to rewrite the url, that is when your server gets the url, it rewrites it with port number (8080).
First of all change Listen 8080 to Listen 80, as you want your application to be accessible only with http. In your http-vhost.conf file put following lines (of course after removing previous changes). In the following configuration yourDefaultHttpFolder means the default http folder. You might have changed it. So correct it depending on your system.
<VirtualHost *:80>
DocumentRoot "/Applications/mampstack-5.4.20-0/apache2/htdocs/yourDefaultHttpFolder"
ServerName 127.0.0.1
ServerAlias localhost
SetEnv APPLICATION_ENV development
SetEnv APPLICATION_DOMAIN localhost
<Directory /Applications/mampstack-5.4.20-0/apache2/htdocs/yourDefaultHttpFolder>
RewriteEngine on
RewriteCond %{SERVER_PORT} ^80$
RewriteRule ^ http://%{HTTP_HOST}:8080%{REQUEST_URI} [P]
</Directory>
</VirtualHost>
<VirtualHost *:8080>
DocumentRoot "/Applications/mampstack-5.4.20-0/apache2/htdocs/mext-pst-dashboard/web"
ServerName mext-pst.local
ServerAlias mext-pst.local
SetEnv APPLICATION_ENV development
SetEnv APPLICATION_DOMAIN mext-pst.local
</VirtualHost>
This configuration is working on my server, when ever I try to access using 80 it rewrites the URL to my 8080 port and I see the content of that folder, not the the default index page.