The hardware is there (RPi + USB storage). The server software is there (NextCloud, Plex, n8n, etc). What isn't there is the plumbing. The next logical step after this blog post is making your services accessible to your phone over the public net. You'll immediately find yourself mired in domain name registration, VPS management, TLS cert management, dyndns, port forwarding, hole punching, etc etc. There are lots of…
PageKite (https://www.pagekite.net) is what it sounds like you're looking for. It'll set you up with a url, SSL, and a tunnel in about 30 seconds. Highly configurable for your own domain if you'd like, multiple ports etc.