Found this in AIM 5-3-1
(a) When operating in a radar environment: On initial contact, the pilot should inform the controller of the aircraft's assigned altitude preceded by the words "level," or "climbing to," or "descending to," as appropriate; and the aircraft's present vacating altitude, if applicable.
EXAMPLE-
1. (Name) CENTER, (aircraft identification), LEVEL (altitude or flight level).
2. (Name) CENTER, (aircraft identification), LEAVING (exact altitude or flight level), CLIMBING TO OR DESCENDING TO (altitude of flight level).
NOTE-
Exact altitude or flight level means to the nearest 100 foot increment. Exact altitude or flight level reports on initial contact provide ATC with information required prior to using Mode C altitude information for separation purposes.
In the terminal environment (contacting departure) using this phraseology would work.
Departure, Cesna 123, leaving one thousand eight hundred, climbing to five thousand five hundred.
Departure, Southwest 123, leaving two thousand two hundred, climbing to flight level one eight zero.
Departure, United 123, leaving five thousand, climbing to one zero thousand.
With the correct phraseology, it makes you sound confident, professional, concise and removes all ambiguity.