In a 1- to 1 1/2-quart pan over medium-high heat, bring maple syrup to a boil. Reduce heat and simmer, swirling pan occasionally, until reduced by about a third, 10 to 12 minutes. Pour into a glass measure nested in a bowl of ice water and stir constantly until syrup is very thick and barely warm to touch, 3 to 4 minutes. Remove from ice water. In a bowl, with a mixer on low speed, beat cream cheese and butter until well blended. Beat in powdered sugar. Scrape in reduced syrup; beat until smooth.