I'm sorry to hear about your fellow's swollen ear.
Does this swelling feel like a water balloon?
Is it part of the ear flap?
Has he been shaking his head?
Does he now or has he ever had an ear infection?
Does it look like the dog in this link below? (can be smaller but this will give you a general idea) https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSP22YeYjTDsYPXpDMZCd5QG6g7BWmHlY59N2ZcNY7t_OfZh7qG
If so then this is likely an ear hematoma. This happens when a blood vessel in the ear breaks and the area inside the ear flap fills with blood.
It is usually from them shaking their head/ears repeatedly from an ear infection.
But sometimes they just shake their head a few times, hit the ear on something and a blood vessel breaks leading to bleeding.
If it is very small (nickel size) it may heal on its own just fine as the blood is reabsorbed.
You can apply a cool compress for 5 to 10 minutes at a time to the swollen area the first 24 to 48 hours, then pat dry and apply cortisone cream (like cortaid) twice daily to help reduce inflammation.
After 48 hours try a warm compress rather than cold to speed healing and improve circulation and then cortisone ointment.
But if it's larger then it may need to be drained and/or sutured so it doesn't refill.
If you notice any odor or increased waxy debris then he may have an early infection which started all this, and then he should definitely see his veterinarian for proper treatment no matter that size of the swelling is.
Keflex is good for skin infections, but will not reduce the swelling. Ear infections are best treated with topical medications instilled into the ear itself, oral antibiotics are rarely prescribed as they cannot effectively cross thick ear skin to get to the infection.
If he has a secondary skin infection from scratching his ear he may need antibiotics too, but he will need ear medication too.
If he is scratching at his ear quite a bit or seems bothered by the swelling you can give him Benadryl (diphenhydramine) at a dose of 1mg to 2mgs per pound of body weight orally every 8 hours (two 25mg tabs per 50 pound dog every 8 hours). This will reduce allergic itchiness and can make him sleepy which should help him leave the ear alone.
If he is rubbing the ear or scratching at it placing an elizabethan (lampshade) collar is recommended so he doesn't further traumatize his ear, which could enlarge the hematoma.
Please let me know if you have any further questions.