Pothos, like most Aroids, is considered toxic because the plant tissues contain calcium oxalate crystals. Depending on the concentration they can cause symptoms ranging from mild discomfort to death when eaten, but pothos is definitely on the lower end of that range. My cats eat it every time they can manage to grab some. The vast majority of toxic plants do not cause issues for frogs because the frogs are not consuming them, the only one I avoid is Dieffenbachia because the concentration of calcium oxalate in the sap is high enough that it can cause skin irritation on contact.