I’ve worked the speed on one and had to input text into others. And there being phonetic text was a rare occurrence and only for technical terms or very uncommon words. And 100% sure „pantries“ would not be one of them.
Maybe there are systems that do this (which I think is highly unlikely, as it would make it harder for someone reading common words displayed as phonetic in sentences), but I wouldn’t go as far as saying: „Teleprompters are also phonetic.“ Btw what’s your source on this?
My guess would be that, as while we are reading text fast, we don’t actually read all letters or their proper order in a word, but our brain just quickly scans the letters and context and outputs what it makes out to be the right word in this situation, this was just a misinterpretation. The other option could be that somebody made a spelling error and „panties“ was actually displayed on the prompter.