This code snippet is taken from https://github.com/aminography/CommonUtils/blob/master/library/src/main/java/com/aminography/commonutils/ContactUtils.kt I take no credit for this snippet. I'm just using it for my blog.

ContactsContract-GetAllContacts.kt

// First, we define a structure to store contact data we want to retrieve
data class ContactData(
    val contactId: Long,
    val name: String,
    val phoneNumber: List<String>,
    val avatar: Uri?
)
  
// Here are the functions to retrieve all contacts matching the search pattern 
fun Context.retrieveAllContacts(
  searchPattern: String = "",
  retrieveAvatar: Boolean = true,
  limit: Int = -1,
  offset: Int = -1
): List<ContactData> {
  val result: MutableList<ContactData> = mutableListOf()
  contentResolver.query(
      ContactsContract.Contacts.CONTENT_URI,
      CONTACT_PROJECTION,
      if (searchPattern.isNotBlank()) "${ContactsContract.Contacts.DISPLAY_NAME_PRIMARY} LIKE '%?%'" else null,
      if (searchPattern.isNotBlank()) arrayOf(searchPattern) else null,
      if (limit > 0 && offset > -1) "${ContactsContract.Contacts.DISPLAY_NAME_PRIMARY} ASC LIMIT $limit OFFSET $offset"
      else ContactsContract.Contacts.DISPLAY_NAME_PRIMARY + " ASC"
  )?.use {
      if (it.moveToFirst()) {
          do {
              val contactId = it.getLong(it.getColumnIndex(CONTACT_PROJECTION[0]))
              val name = it.getString(it.getColumnIndex(CONTACT_PROJECTION[2])) ?: ""
              val hasPhoneNumber = it.getString(it.getColumnIndex(CONTACT_PROJECTION[3])).toInt()
              val phoneNumber: List<String> = if (hasPhoneNumber > 0) {
                  retrievePhoneNumber(contactId)
              } else mutableListOf()

              val avatar = if (retrieveAvatar) retrieveAvatar(contactId) else null
              result.add(ContactData(contactId, name, phoneNumber, avatar))
          } while (it.moveToNext())
      }
  }
  return result
}

private fun Context.retrievePhoneNumber(contactId: Long): List<String> {
    val result: MutableList<String> = mutableListOf()
    contentResolver.query(
        ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
        null,
        "${ContactsContract.CommonDataKinds.Phone.CONTACT_ID} =?",
        arrayOf(contactId.toString()),
        null
    )?.use {
        if (it.moveToFirst()) {
            do {
                result.add(it.getString(it.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER)))
            } while (it.moveToNext())
        }
    }
    return result
}

private fun Context.retrieveAvatar(contactId: Long): Uri? {
    return contentResolver.query(
        ContactsContract.Data.CONTENT_URI,
        null,
        "${ContactsContract.Data.CONTACT_ID} =? AND ${ContactsContract.Data.MIMETYPE} = '${ContactsContract.CommonDataKinds.Photo.CONTENT_ITEM_TYPE}'",
        arrayOf(contactId.toString()),
        null
    )?.use {
        if (it.moveToFirst()) {
            val contactUri = ContentUris.withAppendedId(
                ContactsContract.Contacts.CONTENT_URI,
                contactId
            )
            Uri.withAppendedPath(
                contactUri,
                ContactsContract.Contacts.Photo.CONTENT_DIRECTORY
            )
        } else null
    }
}

private val CONTACT_PROJECTION = arrayOf(
    ContactsContract.Contacts._ID,
    ContactsContract.Contacts.LOOKUP_KEY,
    ContactsContract.Contacts.DISPLAY_NAME_PRIMARY,
    ContactsContract.Contacts.HAS_PHONE_NUMBER
)