Hi and welcome to the forum!
First off, it's not uncommon for flowers towards the tip of the inflorescense to be a little smaller than the first ones to open. So a little variation in size is normal.
Secondly, Phal flowers often don't like a change in environment. Sometimes just the change in environment form nursery to home will cause buds to drop off. it's possible, as you suspected, the warmth caused buds to open early and therefore be smaller. the next time your Phal blooms it may not do this since all your flowers will be opening at home instead of half at the nursery and half at home.
If you don't have a good culture sheet for Phals, go to
www.aos.org and get a Phalaenopsis culture sheet. With good culture your plant should bloom again for you. Typically Phals bloom once a year but the flowers last a long time.
Give the culture sheet a good read and if you have questions let us know.
Happy Growing!