How to call colleagues who was once your professor or advisor?
[ My updated answer after the OP updated his location and more info. ]

First, congratulations on your Ph.D. That is wonderful. :-)

In Asia, in generally, you probably should always call people, who once were your professors, with the title &quot;Professor/Teacher/Doctor&quot; at colleges, at commercial companies, or even in general social settings.
Note: Even if they are no longer your professors now, and they are working either at the same colleges or in the business environment with you as co-workers, perhaps, it is still a good idea to call them &quot;Professor&quot;.
Generally speaking, that shows the respect and gratitude toward your former teachers/professors in Asian culture.
In my country in Asia, I have seen one University professor calls his former college instructor &quot;Professor/Doctor&quot; all the time. They are both teaching at the same college now, and getting along very well as both co-workers and former teacher/student.