Less phone usage makes for less phone usage. It gets easier. Now I don't particularly care what the messages are if they come outside of my designated "message checking time."

Anecdotally, I'd give it 3 months of "reduced phone usage mindfulness." For further reading, check out the wikipedia article on ∆FosB expression, which is a gene expression which essentially tells your body to keep doing things that release dopamine. It takes about 3 months for the ∆FosB expression to decay.

In my experience turning off my phone solves the temptation to check it. The friction of having to turn on my phone is small but apparently enough.