"The lantana looks like it is dry as the leaves look a bit brown but I don't think it is a problem of too little water"

How are you watering it?

Have you tested the soil with a moisture meter?

Don't feel bad. I've had the same problems with all colors of lantanas. They should be simple to grow but normally only last one season for me and then they don't make it through the winter. My guess is that I overwater them.

I can't get rid of mine! I removed about a dozen of them, and between the roots left in the ground and the seeds they keep volunteering. They really don't need much water at all once established. Believe me, the ones I have are not getting pampered.

lantana is a wonderful plant for phoenix. we see them growing in the hottest places. I would guess that for some reason your soil in that area is not agreeable. Id get a couple of buckets.. pick up the rocks, put in a bucket.. dig up the soil and discard it.. take soil from another place.. put some peat moss or mulch in it and plant another and then return the rocks. You don't know if at sometime in the past someone poured out something noxious to plant growth.

I'm shocked to see anyone struggling to keep lantana alive. It's invasive in my yard, I do my best to murder it 3x a year and it comes back happy as ever, in spots of my yard that have concrete-clay soil and literally never get watered. That makes me think maybe you could be overwatering?