I have to talk a lot at work. how can i protect my voice?

Plent of water: Drink plenty of water. Avoid caffeine - it dries out your saliva. If you have symptoms of acid reflux... Get it treated. And rest your voice if you don't have to use it.

By speaking properly: Speaking is like anything we do. It can be done well or done poorly. There is a proper way to speak involving good breathing and "support" combined with a relaxed neck and voice box. A lot of people don't breath properly and "squeeze" or tense their throat muscles when they speak. These people will feel tired and uncomfortable after speaking a lot. A speech therapist can fix this.