I need a semi rugged case which is slim enough for a road jersey pocket, dust sweat and splashproof, yet easy to put on/ take off between rises and not expensive.

Any recommendations?

Which iPhone? 7 is already dust/waterproof.

6s

Life proof is probably the best but I wouldn’t fancy taking it on/off regularly.

One of them phone/card wallet things that rapha and the like do?

Mine lives in its Lifeproof Nuud case pretty much permanently. Previous 5s came out of one after 2 years looking brand new.
Has survived 8m drop to concrete, drop on bike at 20ish mph and a 30deg wash cycle.

Life proof for me – not nuud, the other one. Had it on my 6 for a few yrs and water/ drop/ idiot proof. No real need to take on/off as it’s pretty slimline. Does come off easy with a 5p coin though.