Cant say ive ever found myself needing to carry stuff in my bibs.
But i wear a jersey so it hasnt come up before.
...and when I don't wear a jersey and instead wear a tech tee, I just use my under saddle bag which is 6-7.5liters, depending if its expanded. I used it for longer rides and just stopped caring if its on the bike at all times.
Stays out of the way and doesnt make me carry too much in my jersey.
But hey- lots of options are great in life.
These rapha bibs look similar in style and intent to the currently popular women's athlesure yoga pants that have a built in cell phone pocket.