You need to install podman (an alternative to docker present on fedora 31+), to build correctly epitest-toolbox image.
Furthermore, this image is meant to be used with toolbox. Toolbox is a way to develop in immutable systems such as fedora silverblue.
This toolbox image doesn't contain php because of httpd's incompatibility with rootless containerisation.
Build the image with podman :
cd HUB_epitest_toolbox_2020
podman build . -t epitest-toolboxUse it within the toolbox environment :
toolbox create -i epitest-toolbox