Hi @busean,
I guess you can achieve that in few different ways:
a) If not approve you can have a service task or script task that calls your php scripts and tells it to continue
b) If not approve you can have an external task (https://blog.camunda.org/post/2015/11/external-tasks/) and implement a worker in php that checks the external task queue regularly for new work
Hope this gives you some ideas on how to continue.