Every nurse is different when it comes to how/when they like certain info to be reported. For example, many nurses would rather have all the blood sugars you took at once than you calling with each sugar as you take them. Some nurses want to be alerted of every blood sugar you took while others want to know the abnormal numbers. It helps asking the nurse who you are concerned about how they would prefer things done. After all, you'll be working them on an almost daily basis. You and your nurse are a team so you have to be assertive with them so you're both on the same page about the patient. If there is anything that your nurse asks of you(like putting in a foley) and you feel unconfortable doing it, speak up!
I've been told that I have a soft voice, but I try my best to avoid sounding timid on the phone when I'm speaking to other nurses, physical therapists, dietary, etc.., because my message needs to come across the best way possible to make sure my patient is being taken care of. I'm still working on the soft voice too. But I think having a soft voice helps to calm patients. When overcoming shyness, I'm trying to focus on what I'm saying so that I can come of as assertive.
On another note, whenever I notice that the nurse is talking to someone else and I have something to them(maybe a patient's BP is 204/99), I wait until the conversation is finished. They may be in the middle of giving report while I'm taking vitals so in that case, I might mention the BP and tell them I'll enter the rest in the computer for their reference when they finish report. Some nurses don't like being bothered at all during report, maybe because they have a lot of information going on all at once. However, I would rather let them know before something happens and someone asks me why I didn't let the nurse know ASAP. I think you should use your best judgement and observe who you are working with. With time, you will get there.
The only people I still feel kind of intimidated by are doctors, only because even nurses seem to dislike them. I don't know how to deal with them myself when I become a nurse.