I worked for a small company where the owners at times were stuck on phone calls through lunch and would ask someone who didn't have an immediate deadline coming up to get them food, and provide money for that person to get themselves food as well. It was nice because we would have been willing to pick something up for them anyway without them paying for our food, too.
When the admins were out picking up supplies, sick or whatever, we would fill in answering the phones. Because there were incoming service calls they had to be answered.
Rather than being insulted, we all felt it was part of chipping in to get what needed done. Certainly had getting lunch or answering phones kept us from doing our own jobs we would have explained to the owner that it was interfering and been exempt from requests, and there were times that was the case for everyone.
I think there's an attitude problem in the office, whether it's yours or that of the bosses. I don't think being asked to chip in with answering phones is a problem at all.