Transfering MS in math credits to a PHD program

Any thoughts or experices about how easily and how many credits from a two-year 30 credit MS in math program would transfer to a PhD program?

It’s from a very credible school, which itself does not have a PhD program, so the quality of the courses should not be an issue. And the school says its degree is good for those wanting to go for a doctorate.

I looked at a couple of PhD programs, and one said essentially no transfer credits, another said it depends.

One of the reasons for looking at an MS program rather than to go straight for the PhD would be to burnish the resume of a late blooming undergraduate possibly to gain admittance to better doctorate program.

I know that grad schools have requirements for time in residency, as well as more venal interests in $. And that in the end course requirements can be a fraction of the time to get the PhD.

As you have discovered, it depends on the program. Some programs give credit but still require you to take all the coursework. Other programs will give credit and waive duplicate coursework (my university, Illinois Tech does this), and others will give no credit and no course waivers. However, you should not go into a Ph.D. program which will not support you fully with tuition and stipend, particularly in a STEM field.