Unfortunately supervisors often say one thing and do another, the infamous “my door is always open” often translates into “my door is always open, but I don’t want anyone coming through that”, the manager who tells you they welcome feedback are often the most sensitive, etc.
A lot of the time it comes down to your approach, someone who is sensitive to criticism or in feeling like they are being attacked have to be handled in certain ways. For example, if you say to this person “You asked me to dial into this meeting, and calling that number costs me money” it sounds like a personal attack, but if you submit an expense report for the calls, and then point out that using that number will cost the company money, as someone else said, and suggest maybe finding a conference that has local access or an 800 number might be more cost effective, it becomes about process. One thing to note, if the number involved is in the US, most people these days have plans with unlimited local and long distance calling, whether through VOIP or through landline or cell service, so they might not even think that a call would cost anything extra.
Likewise, when it comes to correcting a document, some people get upsets if you correct the words in the document and give it back to them. A better way may be “Hey, I looked over the document you sent me, and I had some thoughts on how it might be improved if you would like”, it turns from being (in their head) “You screwed these sections up” to being a colleague suggesting improvements.
Unfortunately there are always difficult people in the workplace you have to deal with, what seems trivial to you might be a big deal to them, have had to deal with that with both bosses and people reporting to me over the years, and it can be hard and frustrating how to avoid the minefields, and often with people like that the big thing is finding a way to criticize or give feedback without seeming to. One rule I learned (from a book on being the parent of a sport kid, written by Cal Ripken, Jr) is to sandwich feedback’/criticism in between compliments, so say something “Hey, X, I think that document you sent to me was really clear and well written. I do have a couple of suggestions that I think may help improve it, but overall I think it really got the job done”.