Blood in phlegm

It could be something minor like a small burst blood vessel from coughing hard, or it could point to something that needs attention, so it is hard to say without a proper check. At 24 months, I would not wait too long on this one since toddlers cannot really tell us how they are feeling. It might be worth bringing her to the PD soon just to rule out anything more serious, and if the bleeding increases or she develops a fever, I would go sooner rather than later.