PhD => Doctor. Doesn't matter if they are a Lecturer, Senior Lecturer, Professor etc., the academic title of Dr. is awarded to anyone with a PhD (or alike, such as an SJD or a ThD etc.).
The title/rank of Lecturer, Senior Lecturer, Associate Professor, Professor etc. are awarded by the institution. Associate Professor or Professor do have PhD's, but a Lecturer and Senior Lecturer may or may not have a PhD. So don't just call anyone a Professor.
For Bachelors and Masters, the title is simply Mr/Miss/Mrs etc.
Everyone will have their own preference though, if you're not sure, you could just Google their university profile and see their rank/title. Or you could just call them by their first name.