In any case, your profession has put you at greater risk of nuisance calls, so again, you have more reason than the aversge person to guard your number carefully. For people without much risk, as I say, it seems silly to me.
It's very nice that you're in a position where you can say that. You've never experienced any of the negative things that can happen when your contact details get into the wrong hands. I imagine you've never had to deal with completely changing your main contact methods in a hurry, or else you had an incredibly easy time of it since you're able to dismiss it as 'simple'. That's really, really nice... for you. I honestly hope you never have to learn differently.
The OP isn't in that position. She has a reason for wanting her number to be kept private and she's taken all the steps that should have kept it private - it's unlisted, she's jumped through the hoops to keep it secret at this organisation, and she signed up for this volunteering gig through the system that is SUPPOSED to have her number flagged as 'not to be released' - and for whatever reason, it hasn't worked. Either the system didn't flag it, in which case this needs to be reported so that the system can be fixed (and the list should be withdrawn, and there should be a sincere apology), or the system DID flag it but the coordinator ignored that, in which case oh boy we have a bigger problem here.
This is why the release of personal information HAS to be opt-in, if you ask me. I have no particular reason for having my phone number secret, but I still don't want it out there. When I was at uni, we had anonymised ways of contacting other students, so the guy who wanted to borrow my lecture notes could ask me - good - but if he was a little off kilter and thought I was stunningly beautiful and should be his girlfriend and sure I'd said no but he KNEW I'd change my mind if he just followed me around town for weeks and asked me out three times a day, he didn't have anything that could lead to him getting my home number or address. No, that is not a random example. I had absolutely no reason to expect that giving my phone number or home e-mail out to my classmates might be a bad idea, and they certainly had legitimate reasons to need to contact me, so by your reasoning it would have 'seemed silly' to keep my details secret. The university protected my personal information anyway, and oh boy was it ever a good thing they did!
Finally, Teenyweeny, I have to take issue with your repeated dismissal of other people's reasons for wanting to protect their personal contact details. In the end, it doesn't matter whether or not they have a reason that seems 'good enough' to warrant doing so - if they want to keep their phone number etcetera private, they should be able to and everyone else should respect their wishes... no matter how 'silly' it seems.