The volume measurement for AmesPhos is 1/4 to 1/2 teaspoon per pound, so you were double the amount, which I would guess can't contribute to the dryness. Now, phosphates are dissolved in little water before adding it to the meat. In theory, this would reduce the amount of icy water called in the recipe, but all you are really looking for is a sticky texture. After it rests overnight the liquid equalizes anyway.
A chuck is between 80:20 and 75:25 and a lot of all beef sausages are higher than that. Or you can add some ground pork.
Another finishing option for smoked sausage has always been poaching, and this is how a lot of hot dogs, smoked kielbasa and summer sausage is finished.... but it's the 21st century. Do you happen to have a sous vide circulator? For 5 or 6 years sausage makers have been cold smoking their sausage (with cure), bagging it (some don't even bag it) and put it into a sous vide bath for the finish. With poaching or sous vide it's impossible to over-cook it and it stays really moist. I cure brined some chicken breasts for lunch and salad meat and cool/hot smoked it today for 2.5 hours until the internal temp was 100°. Now I have it in the sous vide container at 147°. It will take 60 to 75 minutes to pasteurize the chicken and make it safe. Beef or pork sausage can be SVd as low as 152° for an hour or so and will be pasteurized, but texture wise some go to maybe 158°. You just need to find a sweet spot.