I can’t speak for an education consultant but being an education consultant in Australia, I would assume it is quite similar across countries.
My response is based on Australian university and keep in mind that this only refers to the general PhD admission, not with scholarships or financial aid.
I think there are two deciding factors for your PhD admission
Your research experience. This can be demonstrated in various forms
Honours year
Major (or even minor) thesis completion
Article(s) published
The support from your [potential] supervisor
To my knowledge, an educational consultant basically consults you on your education pathway, files your documents, fill yours application and submits to the university. The consultant is unlikely to have an impact upon your admission probability (particularly in prestigious universities).
For me at PhD level, a student should be capable of contacting potential supervisor. That student should be capable of doing prior ‘research’.
So no, I don’t think educational consultant is a deciding factor for a PhD admission.