The Favorites and Recents lists in the Phone app are great for making quick calls and returning missed calls, but if you want to add new people to Favorites you can. Tap the Favorites tab then tap the + icon. From here select a contact to add to your favorites.
For more options, tap the “i” button next to any entry in the Favorites or Recents lists. Here you’ll be able to contact that person back on any of their numbers or by email or text. If viewing from Recents, you can add them to your Favorites list, or add the number as a new contact or to an existing contact.