"Front desk agent" sounds very unnatural to me.
I would say that "receptionist" would be the correct word for someone whose permanent job is to greet clients or guests as they enter a business or a hotel.
If someone had various tasks on their job description and greeting people was just one of them which they did perhaps only once a week, they might say something like:
On Mondays, I work in the back office doing the accounts. On Tuesdays, I work on the front desk. On Wednesdays and Thursdays I'm in charge of the catering staff and on Fridays, I cover housekeeping.