It’s not the most robust example, but this part of the docs covers everything you need to know to make an HTTP API access smart app. Definitely not intended for non-developers, but it covers exactly what you’re trying to do.
To see a working HTTP API smart app example, look at this Groovy code for this dashboard app. (See the project documentation for more details)
The PHP part that you’re referring to is just the remote side that communicates with SmartThings (Tasker is that part in your case - although you still need to sort out OAuth authentication). You could implement that with any client and/or server side code that is capable of making HTTP calls and handling OAuth authentication.