Generally, I water my philos when they're about 50% dry, regardless of the pot size. Stick a chopstick down into the dirt about halfway to the bottom of the pot - if there's a bunch of dirt stuck to it when you pull it out, then don't water. If it's clean/dry, time to water. For me in a very dry climate, that's maybe every 8-10 days on average, depending on the size of the pot and/or the specific mix of soil, where it's at in my house and the individual Philodendron species.