I feel so guilty

My mom asked me what I want for Christmas so I gave her a link to some phone cases and she already bought them. She’s switching our family over to Verizon so we are getting a free iPhone 7 and is gonna give it to me (because I have the oldest phone in the family and need to be upgraded) and I really want the phone but I could just let my older sister take it because she doesn’t have phone cases ordered for her for Christmas. I want it but I don’t want to burden my mom with returning the cases and getting larger sizes on amazon. I feel so guilty that I want it.

Am I being selfish wanting the phone? My mom said it was ok but I still think it’s rude.

What should I do?