What does this Cantonese sentence "冧哥覆咗你未?" mean in English?
冧哥 (the subject) roughly means "Mr. Sweet talk" (冧 has the meaning of "sweet talk" or "coax"; adding 哥 to the end of a noun is a common way to nickname someone. )

覆咗 = replied (覆 is short for 答覆; 咗 is a word particle that indicates the verb is completed, It functions the same as 了 in Mandarin)

你 = you (the object)

未 = has not/ not yet 

"冧哥覆咗你未?" = "Mr. Sweet talk replied you? (or he) has not?" = "Has Mr. Sweet talk replied you yet?"