Listening some RTs, I heard ATCos reporting airways, for example: UL65, UPPER LIMA 65. But the phonetic alphabet says UNIFORM. Why do they say like this, please? Is there any manual in which we can study these differences?
ICAO Annex 11 and Doc 4444 confirm the usage of Upper.
Airways are four groups per ICAO, the older group is A, B, G, and R. Those stand for Amber, Blue, Green, and Red. There are three other groups.
So an airway named UG1 will be called Upper Green (not Golf) One on the radio.
Example they give in Doc 4444:
N0450F310 L9 UL9 STU285036/M082F310 UL9 LIMRI
(...) the flight will proceed on Airways Lima 9 and Upper Lima 9 to a point bearing 285 degrees magnetic and 36 NM from the Strumble VOR. From this (...)
Jeppesen Airway Manual also confirms it, check page 251:
FAA (for airways only)
Q is called Q (kyo͞o) on the radio (not Quebec), J is called J, not Juliet or Jet (Jet is what it means). See FAA JO 7110.65X 2−5−1 AIR TRAFFIC SERVICE (ATS) ROUTES.
VOR/VORTAC/TACAN airways or jet routes. State the word “Victor” or the letter “J” followed by the number of the airway or route in group form.
EXAMPLE− “Victor Twelve.” “J Five Thirty−Three.”
The FAA is similar in using the color code for the aforementioned group:
Colored/L/MF airways. State the color of the airway followed by the number in group form.
EXAMPLE− “Blue Eighty−One.”
UR5—Upper Romeo Five
UW456—Upper Whiskey Four Fifty Six
Yes the FAA handbook does not agree with their ATC Job Order regarding R being Red (this will be for the old airway system such as those still in Alaska).
Note: the question asks about airways, the information here is not for tail numbers, navaids, etc., only airways.
See here for how the FAA decides on the designations: How are Victor airways defined and numbered?
@JimyPP is correct on the use of Uniform.
In this case (I assume you are listening in Europe) there is such thing as an Upper airway. So the controller was correct in his phraseology
All airspace above FL195 is class C controlled airspace, the equivalent to airways being called Upper Air Routes and having designators prefixed with the letter "U". If an upper air route follows the same track as an airway, its designator is the letter "U" prefix and the designator of the underlying airway.
I'm not really sure what the controller meant by "Upper". The "U" in UL65 might already stand for the word Upper, so he used the entire word instead of the one letter abbreviation.
The phraseology for the letter U is indeed "Uniform" as you can see on the specification of the NATO phonetic alphabet. There is no reference to the word "Upper" and only "Uniform" is correct.
It is important to understand the reason for the phonetic alphabet. It is not intended that plain language words should be abbreviated, then re-expanded using a phonetically pronounced first letter as a code word substitution for the original word. Rather it provides a means to spell out a word in cases where communication is difficult.
If a controller couldn't hear well and misunderstood the word "upper", saying "uniform" by itself would probably not help unless the context was very clear.
For example, an exchange where the phonetic alphabet is useful might go something like this:
Controller: "Say again, did you mean 'udder' like the udder of a cow?"
You: "Negative, I spell - Uniform, Papa, Papa, Echo, Romeo."
Whenever a plain language word exists you should generally use it first, but spell phonetically as necessary to clear up any miscommunication.
The caveat to this is when the phonetic version is in more common use. I am not actually familiar with the term "upper" as it pertains to an airway, but in the US the low altitude airways are referred to as "victor" airways. I am guessing that originally the "V" may have been for VFR, but nobody seems to know or care, or to call them anything else.
If the convention is to say "uniform" instead of "upper" (even if that is what it originally meant...) it is generally easier to follow convention to avoid confusion. In the case cited in the question though, it seems that the plain language word is being used.