This vowel sound is the name of the letter E, and usually the letter E is part of the vowel.
The vowel in “leave” is made with the mouth almost closed and the tip of the tongue almost touching or slightly touching the back of the bottom front teeth, and the middle of the tongue lightly touching the roof of the mouth.
This sound is represented several ways in written English:
ee, for example feed, bleed, and green
ea, for example peach, leap, and meat
ie, for example thief, brief, and berries
y, at the end of a word, for example many, berry, tiny, salty, family, and rainy.
Note, the letter I by itself rarely makes the vowel in ‘leave.’ Click here to read more about the letter I