Upgrading phono stage

Hello all,

I have a modest system that I have been adding and changing in small increments. I am using a Rogue Audio Sphinx V2. I love the sound of this integrated especially for the money. I am wondering how much I have to spend on a seperate phono stage to get a marked improvement from the built in. I have read that many think the built in phono stage for the Sphinx is quite good. I have zero experience with outboard phono stages. The prices are all over the place and I would like to spend under a $1000 but if that is not enough to make a big change then I will wait and go bigger in the future. I am using a Ortofon 2M Blue at the moment.

Thank you