Re: Posting as PhD fellow
Ah, in that case no you don't need a visa at all as EU-27 nationals have free movement in Switzerland for up to 3 months then they must either leave or register as being resident here. As you/your employer have already applied for a permit you'd simply register at the cantonal migration office on your arrival to start the process of getting it issued. And no, as said the permit covers both work and residence.
If you're Croatian however, then you are still considered a non-EU national by Switzerland and will need the Type D visa to enter the country. As said, this will be issued ONLY if your permit application is approved. Croatian nationals are subject to permit quota limitations: 50 B permits and 450 L permits per year are available.