Why aren’t my contacts’ phone numbers coming up when I use the message app to text them?

This is a new problem with my Iphone 6. When I go to the message app and start typing the name of a contact, their phone number does not come up as an option even though it is stored in my contacts. Their email address comes up but not their phone number. To text them, I have to go into contacts, find them, them click on the little “message” icon in order to send them a text.