The young Hungarian pianist Dénes Várjon — whose playing has been winning accolades lately, both in chamber performances and as a soloist — presented a program of largely Romantic-era music at the Phillips Collection on Sunday, and he left no doubt that he is a musician of unusual power.Aside from the immaculate technique and deft sense of phrasing, Várjon brought something far more rare — a tangible sense of character in virtually everything he played, with incisive and strikingly flavorful interpretations of Beethoven, Schumann and Bartók .[…]