OP, I can fully see your frustration with the situation. I've been in situations where I felt similar. I never felt insecure in my job in that I thought I would be fired/laid off, but I felt extremely undervalued and insecure in my position, in that people didn't realize what I did or the skill level needed to do it. Its the feeling of being taken completely for granted. It's one thing if you're being asked to help out in the way that anyone could/would be asked to help out, but it's another entirely if you're being told (directly or indirectly, or even just feel as if you're being told) that your position/skill/abilities are no different than that of the receptionist. There is NOTHING wrong with being a receptionist, and yes of course it requires skills, but it is not the same as other job functions that require more specific skills, training, and experience.
It sounds as if the woman making the decision is who you directly report to? I would talk to your direct manager (either her or someone else) about why you don't feel that answering the phones is the best use of you and your whole department's time. An hour and a half a day is 7.5 hours per week--that's almost a full day of work: come up with examples of what can be done in that amount of time that will be sacrificed for this. And suggest number of the salary of someone your position vs. that of the receptionist. It clearly doesn't make sense for someone who makes $20/hour to do the job of someone they could pay $10/hour to do, for example. I'd also speak about the general sense of moral on the team--with the reorg the team has felt undervalued and displaced, and having the team do the job of the receptionist is only going to serve to further disillusion the staff and lead to job dissatisfaction. However, I would be careful to frame the whole conversation as people are willing to chip in where necessary--especially if it was on a much more limited basis, and didn't single out your department specifically, and there was some recognition of the work your department does overall.
It's all about the situation. At my last job I was so frustrated I was regularly crying (almost always in private) about not being able to get anything done and my boss essentially taking credit for my work. Every single time he had a meeting regarding one of my projects or presented something I had done to upper management, I would be so incredibly frustrated and upset. He got 3 promotions, and I got none, over a period of a year and a half. I only stayed that long for some other external reasons. At my current job, I don't feel like I'm taken for granted, and I don't feel like people are stealing my work and stepping on me for my own benefit. My boss now regularly discusses my projects with senior management and needs to present things I worked on, but I'm never concerned. She's representing me well, and not using me to her advantage.
Just like it would be no big deal to be asked to fill in for the receptionist if you otherwise didn't feel stepped on...but it's a different story if they're already treating you like crap.
"I don't know! I don't know why I did it, I don't know why I enjoyed it, and I don't know why I'll do it again!" -BART SIMPSON