Hello,
Kindly advise if it is allowed to submit a doctoral work in progress of one's own chapters to a conference in order to obtain feedback from a broader audience. I also understand that when the final dissertation is submitted to the university, one needs to acknowledge that the work has not been previously published. Please provide some advice on this topic. Thanks

It's fine to submit your work to a conference before publication in a thesis in the form of conference papers, posters and talks. This is normal practice.

Thank you for confirming. I have always thought that the dissertation should be an original and non-published work. Regards

No it doesn't have to be. Many people publish their data in journals before they submit their thesis. It just needs to be your own work.

You can gain a PhD by publication, when the entire PhD thesis is a collection of articles already published.

Presenting a paper at a conference is not the same as having chapters published in a peer reviewed journal. A PhD should be original work, but feedback from conferences is very helpful and encouraged.