My 6 yr old Vitex has always been healthy but this year the leaves are turning brown especially on the sun exposed areas.

Question

The tree is trying to develop blooms but it looks very dry and brown.

Answer 1

You have not indicated the growing conditions and if the tree has irrigation or not, but that is the first thing to consider, water, too much or too little.

Vitex is a drought tolerant tree, but Phoenix is brutally hot and dry and your chaste tree may need a once month deep watering. On the other hand, they can be overwatered and subject to root rot.
There is a common insect pest, thrips. And a fungal leaf spot disease that is known to infect vitex.
But from what you have said about brown leaves on the sun exposed areas, I suspect water deficit and sunburn drying.

https://www.gardeningknowhow.com/ornamental/trees/chaste-tree/chaste-tree-cultivation.htm