The search in iPhone's Mail.app doesn't find anything. The same problem exists on OS X.
When I search a word I usually get no results. It only works if the word is included in a recent email, let's say 1 or 2 weeks old.
Also, there is an option called "Search on the server". It never worked in the last 2 years.
Why is my search broken when using an Apple client to search Gmail?