Here is my Dockerfile to build and install Phalcon 5.x using docker-compose.
Please keep in mind that this is unoptimized and only for development.
Composer + MySQL, xDebug, Memcached and Redis images are included and basic configuration for development purposes.
Be sure to adjust component versions to your needs.
If using xDebug on Ubuntu - please remember to open port 9003 in the firewall (ufw).