I don't have one of these radios, but as a matter of interpreting the text of the manual, page 8 says that one of the “programmable function key” functions is:
OUTPUT POWER SELECTION KEY
Select the transmit output power
temporarily or permanently, depending on the pre-setting.
• Ask your dealer for the output power level for each selection
From this, I conclude that:
The radio has at least three transmit power levels, two of which are called “Low 2” and “Low 1”. Perhaps if you push that key it will cycle through those names on the alphanumeric display along with one or more “high” power settings.
Likely the reason they are not called something more descriptive is that they are arbitrarily programmable and the decision was made not to display the actual power in watts or dBm.
It might be informative to investigate the programming options for the radio — if nothing else to assign OUTPUT POWER SELECTION to one of the function keys and see how it behaves.