Yes, that's the same flip phone Ellen had way back in comic #16. My relationship with phones is weird.
When I first moved out of my parents' home, I resisted getting a phone for a long time. Then, when it was clear that a phone was absolutely necessary, I got a simple little brick, which I used until it physically stopped working. I then migrated to a little red clamshell, which was what I still had when I started Leftover Soup.
Of course, in 2014, most cellphones - certainly most phones used by relatively affluent twenty-somethings like our protagonists - are of the smart variety, with capabilities roughly on par with a cheap desktop computer. Strange how something can seem like an anachronism after only three years or so.
But then, Ellen works for a computer shop, so she likely has access to all manner of hardware, and the flip phone is just a reliable old standby. And, as we've seen, at least when she's at home, most of her voice calls are made through her PC.
Still, as I've declared, Leftover Soup's sliding timeline is set in a perpetual now until some sufficiently widespread upheaval makes that impossible. Until such time as flip phones become extinct or we all get telepathy microchip implants, I don't think this is a detail that merits retconning.