Node-red will be running on a server somewhere and waiting for some input. So you will need some app on the phone that will send a message to node-red.
From your question, I'm guessing that you haven't much experience with NR so I'd recommend watching this playlist: Node-RED Essentials. The videos are done by the developers of node-red. They're nice & short and to the point. You will understand a whole lot more in about 1 hour. A small investment for a lot of gain.
I have no idea about hosting wordpress pages in node-red but if its HTML, i dont see why not - its just I think this might be new(ish) territory & you'll not have anything to read-up. (where as there are loads of posts and an excellent wiki showing you how to do this in VUE with UI Builder)
In ui-builder, you can create a VUE SPA (or any other framework - or infact no framework if you want) - but essentially, the logic and webserver live in node-red and the web page opens on the android device, scans the TAG, feeds it back.
If this is your first venture into node-red and web programming - there are a few diciplines to learn and this is not your basic hello world.
Best advice i can give is get a web page working, then get values from a simple input or button passing back to node-red then embark on connecting up the NDEFReader API last.