Celestia looked through the bookcase, a frown on her face.
"Where is it? I know I saw it the other day..." She sighed. "Luna probably moved it..." At that precise moment, to her utter surprise, her sister then came galloping in, running rings around her sister.
"Tia, Tia, Tia, guess what?" she cried out, jumping up and down. "Did you know that when a Phoenix dies, it turns to ash?" Luna held up the book to the page and tapped it with a hoof enthusiastically. When Celestia turned her head and scowled, her grin fell.
"Luna, I was looking for that!" Celestia yelled before she snapped the book from her sister’s grip.
"What for?" she asked.
"I found a baby phoenix and was trying to find that book so I can see what food she can eat."
Philomena cocked her head at the young alicorn. She looked worried. Celestia saw the baby phoenix's expression and quickly read the page her sister mentioned.
"Associated with the sun, a phoenix obtains new life by arising from the ashes. According to some sources, the phoenix dies in a show of flames, although there are other sources that claim that the legendary bird dies and simply decomposes before being born again. According to some texts, the phoenix can live over 1,400 years before rebirth.
Huh, that's interesting."
Philomena, previously pruning her feathers somewhat without interest, froze. Thoughts quickly began to plague her mind; what if she couldn’t rise? What if, somehow, something went wrong?
Since this is your first fic, I'll be nice and give some constructive criticism.
• Try not to repeat words (aside from generic words such as "and" etc) in consecutive sentences
• "Father" and "mother" need only be capitalised at the start of a sentence or when someone is speaking, e.g: Oh, Mother, why can't I have a purple talking unicorn?
• A phoenix is an animal, it doesn't need to be captalised—unless the baby is called Phoenix
• When you do time jumps, try to make them more obvious. I was so confused at first, I thought Philomena had ran away literally five minutes after being found!!
Other than that, for a first try this is actually pretty well written, although you really need to write longer chapters. As opposed to just having Celestia read the excerpt, have a scene where she looks for the book, for example. Just ways to bulk out the work. I'm also pretty impressed that you've got a decent grasp on writing and formatting dialogue too, kudos (apart from the odd slip-up)!