First Impression
noun
The first (第一) phenomenon is what's sealed into your head. This is your first impression of something.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
オペレーターは、電話をかけてくださったお客様にとって、会社の 第一印象になるということを教えられました。
We were all taught that an operator is the first impression that a caller has of our company.