Taking refuge in the three jewels with respect to DN 26 “Mendicants, be your own island, your own refuge, with no other
  refuge. Let the teaching be your island and your refuge, with no other
  refuge. And how does a mendicant do this? They meditate observing an
  aspect of the body—keen, aware, and mindful, rid of desire and
  aversion for the world. They meditate observing an aspect of feelings
  … mind … principles—keen, aware, and mindful, rid of desire and
  aversion for the world. That’s how a mendicant is their own island,
  their own refuge, with no other refuge. That’s how they let the
  teaching be their island and their refuge, with no other refuge.


DN 26

How is this squared with the Buddhist taking refuge in the three jewels - or at the very least, since the teachings are mentioned, with taking refuge in the Buddha and the Sangha?
The Buddha is the Dhamma; the Dhamma is the Buddha (SN 22.87). 

The Sangha are (only) those realizers of the Dhamma.