Thank you all for your suggestions!
I really did not want another bike bag: got 2 pair of Ortliebs, they are all I need, all my bikes have racks and at least one pannier attached at any time
I might purchase a rack bag at some point in the future, for when I'm 100% sure that I won't stop at Aldi's after a ride.
Anyhow, I really wanted just a very small bag to retrieve my phone on the go, I did not want a bulky one to compete with my already bulky stomach
and I wanted a bit of quality so I won't have to shop again for the same thing in a few months.
@Heltor Chasca put me on the right track: after a bit of Googling I choose
this bag by Osprey, their medium sized Ultralight Camera bag.
When it arrives, I can finally start posting in the Your Ride Today thread without feeling bad that I haven't got pictures!
@wonderloaf your suggestion was good too, but my phone is too big for that bag, I need 16cm length.
Thank you all for your input, it was very much appreciated!
Almost forgot:
@robjh yes, you're a handsome chap (on tour)