Watching buds develop is often an agonizingly slow process. How long it takes will also depend on the temperature, and it's also hard to tell from your photo how mature that largest bud is. My guess is that you have at least another week to wait, and maybe more than that. Some of my Phals grow their buds relatively quickly, while i have one that where it was roughly at the same stage as yours, took a further 3 weeks to bloom.
I think the only think that can be said for sure is 'patience!'
And welcome to orchidboard!