For this case what we should do is fill in the blank with the correct conjugation of the verb between parentheses.
The verb between parentheses is:
Hablar
Suppose that the conjugation time is simple present.
The correct conjugation of the verb for the third person of the singular is:
Él Habla
Therefore, the complete question in Spanish is given by:
¿Por qué habla Juan Miguel por teléfono?
Answer:
"Habla"
¿Por qué habla Juan Miguel por teléfono?