these things are so difficult to explain
but here's what I think :
the 'ö' in björk's name is phonetically for english people written as 'oe' , so the I think the corrent way to phonetically spell björk in english is by-oe-rk.
It's like by-ork but with a a hint of the 'e' sound from jerk in it too. I think an english speaker will stress the 'BY' sound as in 'By-ork' , but a native will stress the vowel 'by-Ork'.