Hope you are doing good!
In this step, you have to create a dockerfile and the base image should be devopsedu/webapp. And you have to write dockerfile in such a way that it should run the PHP application. Please find the below sample docker file which uses devopssedu/webapp as the base image and then it runs the PHP application.
ADD proj /var/www/html
RUN rm /var/www/html/index.html
CMD apachectl -D FOREGROUND
Create a docker file as mentioned above and continue with the next steps of the project.
I hope this helps.