If he mixed it that strong (max it should be mixed is about 10:1) and the haze STILL didn't come off, good chance you're right-- he's going to have to remove and replace the tile. The only thing he could use that would be stronger would be muriatic acid, and as strong as he mixed the phosphoric, and it didn't work, he'd have to have a pretty sharp mix on the muriatic, as well, and then you'd have problems with the fumes ruining other finishes, not to mention the respiratory effects it would have on anyone in the house. You'd be better off to replace the tile.

Bill,
Thanks for your speedy response and advice. Of course, I'm terribly and understandably distressed. I hoped that there would be a positive solution.

I just talked to my tile guy again and he is wanting to try the phosphoric acid at full strength. Can that damage my porcelain and the pebble tile on the floor? He is also consulting with his tile wholesaler. If that doesn't work, we'll have to replace it.

Again, thank you so much for your advice. Like so many others that you've helped, I'm extremely grateful. You contribute so much to this forum!

I wouldn't even think about using it full strength. At that strength, even phosphoric acid fumes can do damage, both to other finishes, as well as anyone in the vicinity, including your installer. Don't let him do it. God forbid he's working without worker's comp (and if he's a one man show, that's legal in most states) and gets overcome by the fumes, he can come back on you for it.

This is going from bad to worse. I plan on taking your advice, Bill, and will let you know how it turns out.

Many thanks.