Extrafloral Nectaries
It's a bit of a mouthful, but that's the name of these dots on this Philodendron Billietiae. Extrafloral nectaries are glands that produce nectar to attract beneficial insects. Extrafloral meaning it has nothing to do with the pollination process while nectaries just define the glands.
This defense mechanism can occur on various plants, but we see it most often on large-leafy Philodendrons.
By attracting beneficial insects, the plant can create a little army to ward off pests. Scientists have observed predatory insects such as ants and ladybugs feeding on the nectar. Of course, since the nectar is 95% sugar, with the remaining 5% making up various nutrients and amino acids, it can still attract pests that enjoy nectar, so make sure to check your plant occasionally for said pests.
In the end, there's nothing to worry about when it comes to extrafloral nectaries. Just make sure to inspect your plants when watering, feeding or the likes.
Click here to see more of these extrafloral nectaries, they look big in the photo but they're actually not that noticeable.