I think one of the best holder I have used.
This multi-functional smartphone holder can hold smartphones up to 6.5 inches and can be installed on car air vent, bike, fitness equipment or table.
It's a 360 degrees rotatable holder, meet your different request.
The outer ring is made of steel and inner ring is of rubber. It gives firm grip thanks to the flexibility of the two rings.
Looking at the grips on the vent, does it sag at all while holding the phone?