Searching for a yaoi manga title (〒﹏〒)

Hi! I'm trying to find a yaoi manga whose name I can't remember. The most I recall is that the plot was "Secretary x Boss." The secretary (seme) is in love with his boss (uke), but I don't remember if he initially admitted or acknowledged his feelings or mistook them for admiration. They both reciprocated their feelings, so I remember the plot being romantic. I also remember a specific scene where the secretary (who wanted to take an exam or a course or something like that, to be a better employee) is taking a call and remembers that his manual said he should smile even if the customer wasn't looking. The secretary had dark hair and the boss had light hair. I remember it's been quite a few years since I read it; it's one of those old manga with a cliché plot, but I really liked it a lot, and I can't remember the name. (〒﹏〒)

Does anyone happen to know which manga could it be?