If you are starting an PhD in Germany, you may have various insurance options at your disposal, depending on your exact situation:
I am doing PhD before finishing my studies
Only students still enrolled into the university, doing the PhD before their masters/bachelor thesis or the state exam can be insured as students in the public health system. If that is your situation you can easily signup for public health insurance as a "University student". If you are receiving a stipend it will not affect your insurance contribution. If you are working for the university or have another employer, it will not affect your insurance contribution as long as it is a working student contract.
I already finished my studies
I have an employment contract with university and earn over €538 per month
All PhD students who have an employment contract with a university and earn more than €538 gross per month are insured through employer. People with yearly gross salary under €69300 are mandatory insured in public health insurance, and the ones earning above can choose between public and comprehensive private health insurance. When signing up, you should choose "Employed" as your occupation.
If, however, you are earning less than €538/month through employment contract, receive stipend (amount irrelevant) or not, you will have the following options:
You can signup for incoming insurance, such as our expat health insurance. It is the most affordable solution, starting at €72 per month. Once you finish PhD and start a regular employment in Germany, you will be able to switch to public health insurance through employer.
If you are currently insured by state anywhere in the EU/EEA, the UK or Switzerland, or you applied for 18d AufenthG - Forschung/Research residence permit, you can sign up for public insurance as a voluntary member. During the signup, simply choose "Other" then again "Other" when asked for your occupation, and follow the instructions. Your monthly contribution will be based on your total income, but not less than €220 per month. Public health insurance provides a broad coverage, but if you do not have any ongoing health issues, choosing expat health insurance might make more sense. Once you finish studies and start a regular employment in Germany, you will be able to switch to public health insurance through employer.
If the stipend accounts for €30 000 yearly or more, you can sign up for private health insurance. Private health insurance works for all visa types and visa renewals and can offer the most comprehensive coverage. If you have pre-existing health issues it might be more difficult to apply.
If you are currently insured in EU/EEA, the UK, or Switzerland you can actually stay on your home insurance for the duration of your studies regardless of your age, there no need to signup for German health insurance. Have in mind that you will need to pass to German insurance once you start earning any income in Germany. If you choose this route read our article on the M10 Meldung. - Only available to people who do not earn any income through employment.