How can you simplify the work on the project interface?

Question

Yii

I am working on a helpdesk project using the Yii2 framework. Briefly describe the principle of operation.
A new request is added (manually or automatically, depending on the source of the output parameters), then notifications are sent to those responsible for it, the request is divided into separate steps with its attachments, responsible, etc. In general, the functionality is typical for this type of project.
Now I'm working directly on the interface of the application. So far, it has turned out to be wild noodles from html markup and php code inserts. I feel that something needs to be done about this, otherwise it will only get worse)
What tools (front-end) can be used to simplify development in this case? Otherwise, apart from jQuery, I didn’t actually work professionally on the client with anything.