I have calle lillies planted under a shaker tree for shade. They seem to have the same problem as yours. Do great in the spring then die back to nothing in the hot weather. They do this every year. I don't think it is the sun per say I think it is the heat. In Calif. I had them in direct sun all day and not a problem. Temp there barley gets above 90 on occasion. Don't worry they will be back.

do they come back when it cools down in the fall? Or not until next spring?

I guess it would depend on where you are. Mine try to come back a little. They don't get much of a chance to grow before they go dorment. It gets cold here by thanksgiving.
So I have to wait tell spring. I thought transplanting them under the tree would help with the heat but no. Every year its the same. I just enjoy them while I can.

If I remember correctly, my calla lillies started coming back around November last year, when it finally cooled off. They grew and bloomed until it got hot, around the end of May.

They're great plants.

they stayed alive through winter?

I have mine in a spot that gets afternoon shade or it is shady in the spot about 1:00. And they always look sickly in July and aug. Then end of Oct. or beginning of Nov. I cut all of the remaining dead stuff off and give them like a tea spoon of a phosphorus fertilizer (water it in) and they have always come back. They usually last until end of Dec. They do not last in our cold cold months. (they do not like to be cold and wet) So I just let them go and then trim them way down almost to like 6 inches in end of Feb. first of March and they come back GREAT!
I hope all of that makes sense!

I have one in a pot that is barely alive. Hoping to transplant to a partly shaded spot as soon as it cools of. It's looked awful since about the middle of June, despite being in full shade. I'm hoping it will recover. I'll give it some bloom booster for phosphorous when I transplant it into the ground, too.

FOLLOW UP----- My Cal's are about 3-4" high. They started to come back week before last. Our temp has been cool at night(62-70)and about 80-95 during the day. This is some what early for them, so I am hoping they will bloom before Thanksgiving freeze.

The one that I have in a pot started growing back out as well. it's got about 3 leaves now and about 8" tall. but the ones that I have planted on the ground still haven't sprouted back out yet.

I'm growing mine in pots and they're coming up now, I think I'll put some in the ground and see how they do.

Mine has started to come back a little from the bottom! When and where should I transplant it?

Tracy- Plant them in the shade if you live anywhere south of the Verde Valley (Sedona) Cals have trouble with the heat. You probley can go ahead and transplant now. Cals are pretty hardy. When you remove them from the pots get as much surounding soil as you can so as not to disturb the new growth or roots, also that dirt will help in the new hole.

Just transplanted mine to part shade today. It has a few sprouts coming back. Can't believe it survived the summer in the small pot on the porch!