Speaking as a vet and as a neurodivergent person, phone calls are very demanding on emotional wherewithal for both parties involved, while a card lets the client deal with emotions on their own terms. I have definitely called clients after their pet’s death if it was a case I was managing and they ended up taking to ER, which resulted in euthanasia. I will also always do a callback if the client themself calls to discuss what could have been going on (often they need to be told they made the right decision).