Diction of phrases.
That is as close as you will get:
Diction - (Merriam Webster) choice of words especially with regard to correctness, clearness, or effectiveness
Diction - (dictionary.com) style of speaking or writing as dependent upon choice of words.
Although this is not quite exactly what you wanted it is as close as you can get for a specific word.
"I have added the phrase 'In essence' to my diction"
The previous doesn't mean "I now know what 'in essence' means", it is much closer to: "I now use the phrase 'in essence' in conversation a lot" or "The phrase 'in essence' is now a staple in my speaking/writing."
If it is absoluetely required that you have a word with the connotation of "I now know", unfortunately (as far as my knowledge extends) there is no word that is specifically referring to the knowledge of phrases, but there are some great general terms you can use, such as:
(My personal favorites to use for this situation would be repertoire or repository)
Please note that the previous words are not to be used as: "I have added 'x' to my repertoire", but rather they are all to be followed by 'of phrases', such as: "I have added 'x' to my repertoire of phrases"