It's not exactly hard, you can download web servers from the Play Store. The problem is that you'll need to set up port forwards and such to get traffic to port 8080 or whatever your web server of choice offers.
Termux can install nginx, PHP, and various SQL clients, so I'm sure someone can make a copy/paste script that'll set up a WordPress server on your phone.
Someone correct me if I'm wrong but I think this port issue will get solved with the introduction of new SVCB/HTTPS RR record types. Basically the dns server will include port info along with existing IP info in it's response.
Termux can install nginx, PHP, and various SQL clients, so I'm sure someone can make a copy/paste script that'll set up a WordPress server on your phone.