"Do you have a cell phone?"
Translation:¿Tienes un teléfono celular?
"?Tienes un celular?" was not given as an option to choose, as I would have picked it. The option given was "?Tienes un telefono celular?". We've been taught that "celular" by itself means "cell phone." Thus "?Tu tienes un telefono celular?" would be translated "Do you have a telephone cell phone?"
"¿Tienes un teléfono celular?" would be the correct word order. Incidentally, in Spain we use the term "(teléfono) móvil" and, more commonly, just "móvil". We would also omit the article and just say, "¿Tienes móvil?". In fact, the indefinite articles "un/una" are often omitted when using the verb "tener" and talking about possessions: "Do you have a car/a house?" would be "¿Tienes casa/coche?".
'Tienes' would be the correct term to use here. In spanish, when you are talking to someone directly, you would use the words with "s" at the end (tienes, quieres, bebes, etc.). When talking about someone indirectly, or when being formal, you would use the same word without the 's' (tiene, quiere, bebe). Also, it would be celular not cellular.