I am trying to make a dynamic web page in the Node-red platform to show realtime sensor value on the webpage. Is it possible to use PHP in Node-red? Any example?
No
There is no PHP rendering nodes for Node-RED.
A quick look on npm only shows one PHP NodeJS node, that hasn't been touched in 7 years and is marked at not working so it is very unlikely that it could be wrapped as a Node-RED node.
Depending on what exactly you want to do, you should look at the following: