I WANNA KNOW THE YELLOW SQUARE TOO but the phone is hinting to Seong-ah that Woo-yeol got his memories back (Seong-ah knows he's the owner of the phone -> tells Woo-yeol that the owner didn't ask for it to be fixed -> Woo-yeol says HE'S asking for it to be fixed because he knows it's Seong-ah's)
I don't get it what's the importance of the phone ALSO WHATS THAT YELLOW SQUARE THING HE PICKED UP GUGHFHDHFS