How do icons get assigned to phone numbers in Contacts

Some phone numbers have both the telephone and text icon. Others only show the phone icon.

Yet I've called and texted both. I sync between an iphone 7+ and Macbook Air. All software is up to date.

Am I adding these differently? Does the choice of mobile, iphone, or location matter?

Some are added directly into contacts; others are added from the texting or phone applications.