I’ve tried to find all of the Schools which include masters students and below, not only PhD students. However, if you happen to be a PhD student, look here and here for tons more opportunities.
Middle East / North Africa
AWSA – The Arab Winter Schools for Astrophysics take place in the Middle East / North Africa each year.
Americas
La Serena – A week long school in August, in Chile, which focuses on Applied Tools for Astronomy.
ISYA – The International School for Young Astronomers is open to graduate and final-year undergraduate students, covering a wide range of topics.
