He occasionally spits up water and phlegm after doing this. He has also started gagging/vomiting small amounts occasionally. We tried maalox which seemed to help one night. His food & water are already elevated. He does have a few 'hot spots' and frequently licks the areas but we try to discourage this.

You have to realize you are dealing with a geriatric dog now and he probably has trouble swallowing. You seem to be coping okay, elevating food and water, good idea. Elderly dogs lose some of their capabilities same as we do in old age. A lot of people don't realize that.
Tick

I have a lab that will be 16 next month. He does this as well. It's old age, like Tick said.

If you are concerned, please see your vet, he/she may be able to offer some suggestions.

Sounds like he is not completely swallowing his drink and has a little left in the back of his throat. Coughing and gagging is the result of something getting in his windpipe. Sometimes dogs get in too big a hurry when drinking and this may be what he is doing... getting too much in his mouth and choking a bit on what he can't get all the way swallowed.

Eating and drinking from an elevated platform is usually done if the dog has a problem with his lower esophagus. If he has this, it may be changing a bit and maybe you could mention this to his vet.