I’ll add additional info for my sake.
I could not connect phpmyadmin when I use Traefik, because Traefik uses the port 8080. So and I created the environment by going through PREVIEW: Using Custom Domains and SSL with Let's Encrypt and Traefik, in such case, the following command worked.
docker run --name phpmyadmin -d --link yourproductname_db_1:db -p 8081:80 --network=wappler-compose_proxy phpmyadmin/phpmyadmin