One way to distinguish between roots and stems (spikes) is to look at the tip. Does it look like it has a bunch of overlapping sheaths/buds (think of tree buds)? If so, it's probably a spike. Otherwise, it's a root. Also keep in mind that most grocery phals, after the initial bloom, will almost always subsequently initiate spikes in the winter, so new growths during the spring/summer are usually roots. The phals we see in grocery stores during the summer have been artificially induced to bloom by changing the lighting and lowering the temperature in the greenhouse.