“What kind of shailos do they pasken via telephone?”
I would think any, other than dinei mamamnos which would require hearing both sides. (though IVe never called)
“Why would someone call a hotline instead of their own Rov?”
1) his Rav isnt available and it cant wait
2) His Rav doesnt know and directed him to the hotline
3) It is a question that he feels uncomfortable to ask his rav
4) He doesnt have a Rav (the answer to your other thread is yes there are many such people)
5) It didnt sound like the Rav got it right
6) He knows his Rav is machmir on this issue and he wants a kulais hoping for a kula
Im sure there are dozens of others i’ll add if I think of others