The number is the same, as far as I know. I think you get an option to press a number for English. If not, most sales representatives can speak English as well. Have booked there many times.

Hi you can reserve online via tickets.oebb.at with the ONE WAY TICKET option and add at adult the discount Interrail/Eurail Global Pass. 

Please note that in July no Nightjet service due to works on the line between Munich/Vienna and Milan/Rome. The only Nightjet service that runs actually is the Munich/Vienna-Venice one. 

You can reserve online unless you have special needs:) 

Most likely-but you did not give any date, so it remains guessing, is indeed that the train does not run-due to works, which plague about all railways anywhere on the continent this summer. And also that OeBB last week announced that about all real sleepers were sold for summer (a few couchette-but /en/ is not that clever in the difference between-are still there)