Thank you for the additional information.
The philodendron plant and fruit can be toxic
to dogs though the toxicity is not life-threatening. Typically this plant causes severe irritation to the mouth and esophagus when swallowed and can cause quite a bit of discomfort overall in the mouth and tongue. The leaves are actually the part that seems to be more irritating though the fruit could potentially cause similar symptoms. Other then mouth and esophagus irritation, you could also see vomiting, drooling, and reluctance to eat or drink.
For now I would recommend using some cold water to rinse out his mouth for up to five minutes. I would not induce vomiting as this could actually make his symptoms worse. Make sure that he is getting plenty of water to drink to help flush out some of the irritants in his stomach
If he does show signs of nausea such as vomiting, drooling, or reluctance to eat/drink then you could give him some Pepcid AC to help with the stomach discomfort. I would give him 5 mg every 24 hours. This medication usually comes in 10 mg per tablet. You can get this medication from a local drug or grocery store over the counter.
Definitely follow up with your vet if he is showing symptoms of any discomfort.
I can definitely look at a picture of what he ate if you'd like though I would recommend rinsing his mouth out either way.
Hope this helps to answer your question - if not or if you have any more questions please feel free to reply by clicking on the "reply to" button. Thank you for your question.