Can LeBlanc, Deceiver be used to clone a Sprite in the Beginning Phase and hold with a Ready Reflection of the new Sprite?

No — not the way you're describing. Temporary kills your Sprite at the start of your Beginning Phase before scoring, so the Sprite is already in your trash by the time you hold and Deceiver triggers (Rule 816.1.b; Rule 315.2 — Beginning Step, then Scoring Step). Since the copy effect needs "another unit there," there's no Sprite left to clone.

The only way it works is if the Sprite is created during that same Beginning Phase after the start-of-phase Temporary check (e.g., you make one in response to another Temporary trigger). Then yes — Deceiver fires on your hold, and you get a ready 3/3 Reflection copy you can use the rest of that turn to move or conquer. But that Reflection has Temporary (Deceiver grants it regardless of the copy, and copying the Sprite also carries its keyword), so it dies at the start of your next Beginning Phase — again before scoring. It can never be the unit that "holds" a battlefield at a later Beginning Phase; use it aggressively the same turn.