I wanted to ask, if it's possible to create a Dialogflow agent chatbot and deploy it as a (PYTHON OR PHP) webhook then use that webhook on different platforms for intergrations.
Dialogflow has two versions, not sure which you want to use (referece).
No matter of version there are possibilities to use APIs. Dialogflow ES has even PHP among supported languages.
No matter which version you will choose, both support REST API's which can be used in any language supporting HTTP and for sure in PHP. As far as I understand language support is just convenient library using REST API under the hood.
All actions that can be done via Dialogflow console can be done with the API's.
Documentation has nice quickstarts for both Dialogflow CX and Dialogflow ES I think this is good start.