Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Symptoms that are not clearly improving deserve further advice, even if they do not appear to be an emergency.
Call emergency services immediately for:
And for anyone, someone who:
Seek urgent same-day care for persistent drooling, increasing mouth swelling, repeated vomiting, signs of dehydration, significant eye pain, light sensitivity, or any change in vision.
Clean up fallen leaves and cut stems promptly.
Arrange routine medical follow-up if mouth soreness continues, eating or drinking remains difficult, vomiting recurs, or a skin rash does not settle after washing and avoiding further contact.
An eye professional may recommend follow-up after a corneal injury.
The article also says
After a mild mouth exposure, follow the poison center's instructions and watch for changes.
The person should be able to breathe comfortably, swallow saliva, and take fluids.
To prevent another exposure, keep calla lilies out of reach of children and people who may chew plants.
Wear gloves when cutting or handling them, wash hands afterward, and avoid touching the face or eyes.
Every sign above is quoted from the sofidex article on Calla lily poisoning. If you are not sure, err upward — it is always reasonable to be checked.