Yes it is going to overwhelm any significantly shorter plants. However if this phlox you have is a tall border phlox and it is well above the height of the geranium when it arrives then there may not be a problem. Other than how the combination of the two looks to you

The phlox jeanna can get up to 5 ft tall, I guess I should of reworded it. I am concerned about the roots and if the Rosanne will effect the branches of it. I was hoping that the Rosanne branches would just grow around the phlox

Yes, that is why I said a tall plant won't be much bothered. If it is tall enough when the stems of the geranium arrive.

The geranium has all its roots near the root crown - the stems don't make a mat of roots underneath. And the stem growth each summer is thin enough that some cut the plant back and start it over about halfway through its summer to fall bloom cycle each year.