Copenhagen University [1] has it as 35,250kr/month, which is almost £4300/month.

Taxes and cost of living are higher in Denmark, but it's still more than double what a student in Britain gets. I had friends studying in both countries, and I was shocked when I found out the difference. (It was all science research.)

A couple of years ago, I saw a job advert at a British research institute I was working with. It was a PhD position, funded and managed by Copenhagen University, but living and working mostly in England to use the special equipment the institution had. The salary was higher than a senior researcher position, also listed, and higher than all the developers I was working with.

[1] https://uniavisen.dk/en/salaries-of-university-of-copenhagen...

I think each country has different laws/rules/regulations for PhD. Where I live it's really common for the job to be tied to teaching hours for instance. It's also easier to do a PhD and live on it than going postdoc (it pays less and there are fewer positions).