When a contact has multiple phone numbers stored on
, you can select which phone number to reply to.
Keep in mind that if you don't select another number, your response will be sent to the phone number that your contact used to send the last message.
Messages screen, tap a contact (or phone number) to display the exchange of messages with that contact.
and select which phone number you want to reply to.
Tap the box that says
Add text, then enter your reply message.